Solve Equations with Fraction or Decimal Coefficients

Solve Equations with Fraction Coefficients

Let’s use the General Strategy for Solving Linear Equations introduced earlier to solve the equation \(\frac{1}{8}\ x+\frac{1}{2}=\frac{1}{4}.\)

To isolate the \(x\) term, subtract \(\frac{1}{2}\) from both sides.
Simplify the left side.
Change the constants to equivalent fractions with the LCD.
Subtract.
Multiply both sides by the reciprocal of \(\frac{1}{8}\).
Simplify.

This method worked fine, but many students don’t feel very confident when they see all those fractions. So we are going to show an alternate method to solve equations with fractions. This alternate method eliminates the fractions.

We will apply the Multiplication Property of Equality and multiply both sides of an equation by the least common denominator of all the fractions in the equation. The result of this operation will be a new equation, equivalent to the first, but with no fractions. This process is called clearing the equation of fractions. Let’s solve the same equation again, but this time use the method that clears the fractions.

Example

Try it.

Solve: \(\frac{1}{8}\ x+\frac{1}{2}=\frac{1}{4}.\)

Solution

Find the least common denominator of all the fractions in the equation.
Multiply both sides of the equation by that LCD, 8. This clears the fractions.
Use the Distributive Property.
Simplify, and notice, no more fractions!
Solve using the General Strategy for Solving Linear Equations.
Simplify.
Check: Let \(x=-2\)

Notice in that once we cleared the equation of fractions, the equation was like those we solved earlier in this chapter. We changed the problem to one we already knew how to solve! We then used the General Strategy for Solving Linear Equations.

Example

Try it.

Solve: \(7=\frac{1}{2}\ x+\frac{3}{4}\ x-\frac{2}{3}\ x.\)

Solution

We want to clear the fractions by multiplying both sides of the equation by the LCD of all the fractions in the equation.

Find the least common denominator of all the fractions in the equation.
Multiply both sides of the equation by 12.
Distribute.
Simplify, and notice, no more fractions!
Combine like terms.
Divide by 7.
Simplify.
Check: Let \(x=12.\)

Condensed: the full section is in OpenStax Prealgebra 2e.

Solve Equations with Decimal Coefficients

Some equations have decimals in them. This kind of equation will occur when we solve problems dealing with money and percent. But decimals are really another way to represent fractions. For example, \(0.3=\frac{3}{10}\) and \(0.17=\frac{17}{100}.\) So, when we have an equation with decimals, we can use the same process we used to clear fractions, multiply both sides of the equation by the least common denominator.

Example

Try it.

Solve: \(0.8x-5=7.\)

Solution

The only decimal in the equation is \(0.8.\) Since \(0.8=\frac{8}{10},\) the LCD is \(10.\) We can multiply both sides by \(10\) to clear the decimal.

Multiply both sides by the LCD.
Distribute.
Multiply, and notice, no more decimals!
Add 50 to get all constants to the right.
Simplify.
Divide both sides by 8.
Simplify.
Check: Let \(x=15.\)

Example

Try it.

Solve: \(0.06x+0.02=0.25x-1.5.\)

Solution

Look at the decimals and think of the equivalent fractions.

\(0.06=\frac{6}{100},\ 0.02=\frac{2}{100},\ 0.25=\frac{25}{100},\ 1.5=1\frac{5}{10}\)

Notice, the LCD is \(100.\)

By multiplying by the LCD we will clear the decimals.

Multiply both sides by 100.
Distribute.
Multiply, and now no more decimals.
Collect the variables to the right.
Simplify.
Collect the constants to the left.
Simplify.
Divide by 19.
Simplify.
Check: Let \(x=8.\)

The next example uses an equation that is typical of the ones we will see in the money applications in the next chapter. Notice that we will distribute the decimal first before we clear all decimals in the equation.

Example

Try it.

Solve: \(0.25x+0.05(x+3)=2.85.\)

Solution

Distribute first.
Combine like terms.
To clear decimals, multiply by 100.
Distribute.
Subtract 15 from both sides.
Simplify.
Divide by 30.
Simplify.
Check: Let \(x=9.\)

Key Concepts

• Solve equations with fraction coefficients by clearing the fractions.
  1. Find the least common denominator of all the fractions in the equation.
  2. Multiply both sides of the equation by that LCD. This clears the fractions.
  3. Solve using the General Strategy for Solving Linear Equations.

Now you Không máy tính nào có thể tính toán được nó, nhưng các mảnh của nó có thể tính toán được. Thử một trong những cách dưới đây, hoặc gõ theo ý bạn.

⌨ Kiểu ✎ Vẽ đi.

Câu hỏi toán của anh.

π Giải quyết

Luyện tập (40)

Đầu tiên thử mỗi câu trên giấy. Cho thấy câu trả lời để kiểm tra; những câu trả lời đã kiểm tra có thể mở trong trình giải cho mỗi bước.

1. Multiply: \(8\cdot \frac{3}{8}.\)

   Làm việc đi. Gợi ý

   Giải đáp

   \(3\)

2. Find the LCD of \(\frac{5}{6}\ \text{and}\ \frac{1}{4}.\)

   Làm việc đi. Gợi ý

   Giải đáp

   \(12\)

3. Multiply: \(4.78\) by \(100.\)

   Làm việc đi. Gợi ý

   Giải đáp

   \(478\)

4. Solve: \(\frac{1}{8}\ x+\frac{1}{2}=\frac{1}{4}.\)

   Làm việc đi. Gợi ý

   Giải đáp

   Find the least common denominator of all the fractions in the equation.
   Multiply both sides of the equation by that LCD, 8. This clears the fractions.
   Use the Distributive Property.
   Simplify, and notice, no more fractions!
   Solve using the General Strategy for Solving Linear Equations.
   Simplify.
   Check: Let \(x=-2\)

5. Solve: \(\frac{1}{4}\ x+\frac{1}{2}=\frac{5}{8}.\)

   Làm việc đi. Gợi ý

   Giải đáp

   \(x=\frac{1}{2}\)

6. Solve: \(\frac{1}{6}\ y-\frac{1}{3}=\frac{1}{6}.\)

   Làm việc đi. Gợi ý

   Giải đáp

   y = 3

7. Solve: \(7=\frac{1}{2}\ x+\frac{3}{4}\ x-\frac{2}{3}\ x.\)

   Làm việc đi. Gợi ý

   Giải đáp

   We want to clear the fractions by multiplying both sides of the equation by the LCD of all the fractions in the equation.
   

   Find the least common denominator of all the fractions in the equation.
   Multiply both sides of the equation by 12.
   Distribute.
   Simplify, and notice, no more fractions!
   Combine like terms.
   Divide by 7.
   Simplify.
   Check: Let \(x=12.\)

8. Solve: \(6=\frac{1}{2}\ v+\frac{2}{5}\ v-\frac{3}{4}\ v.\)

   Làm việc đi. Gợi ý

   Giải đáp

   v = 40

9. Solve: \(-1=\frac{1}{2}\ u+\frac{1}{4}\ u-\frac{2}{3}\ u.\)

   Làm việc đi. Gợi ý

   Giải đáp

   u = −12

10. Solve: \(x+\frac{1}{3}=\frac{1}{6}\ x-\frac{1}{2}.\)

    Làm việc đi. Gợi ý

    Giải đáp

    Find the LCD of all the fractions in the equation.
    Multiply both sides by the LCD.
    Distribute.
    Simplify, no more fractions!
    Subtract \(x\) from both sides.
    Simplify.
    Subtract 2 from both sides.
    Simplify.
    Divide by 5.
    Simplify.
    Check: Substitute \(x=-1.\)

11. Solve: \(a+\frac{3}{4}=\frac{3}{8}\ a-\frac{1}{2}.\)

    Làm việc đi. Gợi ý

    Giải đáp

    a = −2

12. Solve: \(c+\frac{3}{4}=\frac{1}{2}\ c-\frac{1}{4}.\)

    Làm việc đi. Gợi ý

    Giải đáp

    c = −2

13. Solve: \(1=\frac{1}{2}(4x+2).\)

    Làm việc đi. Gợi ý

    Giải đáp

    Distribute.
    Simplify. Now there are no fractions to clear!
    Subtract 1 from both sides.
    Simplify.
    Divide by 2.
    Simplify.
    Check: Let \(x=0.\)

14. Solve: \(-11=\frac{1}{2}(6p+2).\)

    Làm việc đi. Gợi ý

    Giải đáp

    p = −4

15. Solve: \(8=\frac{1}{3}(9q+6).\)

    Làm việc đi. Gợi ý

    Giải đáp

    q = 2

16. Solve: \(\frac{1}{2}(y-5)=\frac{1}{4}(y-1).\)

    Làm việc đi. Gợi ý

    Giải đáp

    Distribute.
    Simplify.
    Multiply by the LCD, 4.
    Distribute.
    Simplify.
    Collect the \(y\) terms to the left.
    Simplify.
    Collect the constants to the right.
    Simplify.
    Check: Substitute \(9\) for \(y.\)

17. Solve: \(\frac{1}{5}(n+3)=\frac{1}{4}(n+2).\)

    Làm việc đi. Gợi ý

    Giải đáp

    n = 2

18. Solve: \(\frac{1}{2}(m-3)=\frac{1}{4}(m-7).\)

    Làm việc đi. Gợi ý

    Giải đáp

    m = −1

19. Solve: \(0.8x-5=7.\)

    Làm việc đi. Gợi ý

    Giải đáp

    The only decimal in the equation is \(0.8.\) Since \(0.8=\frac{8}{10},\) the LCD is \(10.\) We can multiply both sides by \(10\) to clear the decimal.

    Multiply both sides by the LCD.
    Distribute.
    Multiply, and notice, no more decimals!
    Add 50 to get all constants to the right.
    Simplify.
    Divide both sides by 8.
    Simplify.
    Check: Let \(x=15.\)

20. Solve: \(0.6x-1=11.\)

    Làm việc đi. Gợi ý

    Giải đáp

    x = 20

21. Solve: \(1.2x-3=9.\)

    Làm việc đi. Gợi ý

    Giải đáp

    x = 10

22. Solve: \(0.06x+0.02=0.25x-1.5.\)

    Làm việc đi. Gợi ý

    Giải đáp

    Look at the decimals and think of the equivalent fractions.

    \(0.06=\frac{6}{100},\ 0.02=\frac{2}{100},\ 0.25=\frac{25}{100},\ 1.5=1\frac{5}{10}\)

    Notice, the LCD is \(100.\)

    By multiplying by the LCD we will clear the decimals.
    

    Multiply both sides by 100.
    Distribute.
    Multiply, and now no more decimals.
    Collect the variables to the right.
    Simplify.
    Collect the constants to the left.
    Simplify.
    Divide by 19.
    Simplify.
    Check: Let \(x=8.\)

23. Solve: \(0.14h+0.12=0.35h-2.4.\)

    Làm việc đi. Gợi ý

    Giải đáp

    h = 12

24. Solve: \(0.65k-0.1=0.4k-0.35.\)

    Làm việc đi. Gợi ý

    Giải đáp

    k = −1

25. Solve: \(0.25x+0.05(x+3)=2.85.\)

    Làm việc đi. Gợi ý

    Giải đáp

    Distribute first.
    Combine like terms.
    To clear decimals, multiply by 100.
    Distribute.
    Subtract 15 from both sides.
    Simplify.
    Divide by 30.
    Simplify.
    Check: Let \(x=9.\)

26. Solve: \(0.25n+0.05(n+5)=2.95.\)

    Làm việc đi. Gợi ý

    Giải đáp

    n = 9

27. Solve: \(0.10d+0.05(d-5)=2.15.\)

    Làm việc đi. Gợi ý

    Giải đáp

    d = 16

28. \(\frac{1}{4}\ x-\frac{1}{2}=-\frac{3}{4}\)

    Làm việc đi. Gợi ý

    Giải đáp

    x = −1

29. \(\frac{3}{4}\ x-\frac{1}{2}=\frac{1}{4}\)

    Làm việc đi. Gợi ý

30. \(\frac{5}{6}\ y-\frac{2}{3}=-\frac{3}{2}\)

    Làm việc đi. Gợi ý

    Giải đáp

    y = −1

31. \(\frac{5}{6}\ y-\frac{1}{3}=-\frac{7}{6}\)

    Làm việc đi. Gợi ý

32. \(\frac{1}{2}\ a+\frac{3}{8}=\frac{3}{4}\)

    Làm việc đi. Gợi ý

    Giải đáp

    \(a=\frac{3}{4}\)

33. \(\frac{5}{8}\ b+\frac{1}{2}=-\frac{3}{4}\)

    Làm việc đi. Gợi ý

34. \(2=\frac{1}{3}\ x-\frac{1}{2}\ x+\frac{2}{3}\ x\)

    Làm việc đi. Gợi ý

    Giải đáp

    x = 4

35. \(2=\frac{3}{5}\ x-\frac{1}{3}\ x+\frac{2}{5}\ x\)

    Làm việc đi. Gợi ý

36. \(\frac{1}{4}\ m-\frac{4}{5}\ m+\frac{1}{2}\ m=-1\)

    Làm việc đi. Gợi ý

    Giải đáp

    m = 20

37. \(\frac{5}{6}\ n-\frac{1}{4}\ n-\frac{1}{2}\ n=-2\)

    Làm việc đi. Gợi ý

38. \(x+\frac{1}{2}=\frac{2}{3}\ x-\frac{1}{2}\)

    Làm việc đi. Gợi ý

    Giải đáp

    x = −3

39. \(x+\frac{3}{4}=\frac{1}{2}\ x-\frac{5}{4}\)

    Làm việc đi. Gợi ý

40. \(\frac{1}{3}\ w+\frac{5}{4}=w-\frac{1}{4}\)

    Làm việc đi. Gợi ý

    Giải đáp

    \(w=\frac{9}{4}\)

Để cho anh làm việc

Một tài khoản miễn phí thêm ghi chú vào mỗi bài học, ghi chép những gì bạn đã hoàn thành, các bài toán bạn giải quyết ở một nơi, và một giáo viên bạn có thể hỏi về trang này. Toán học là mở cho mọi người, dù có đăng nhập hay không.

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\pmplus or minus
Both signs at once: x = 3 ± 2 means 5 and 1.\neqnot equal
The two sides are different.\leqless/greater than or equal
Inequalities that allow equality; < and > exclude it.\sqrt{x}square root, n-th root
The non-negative number whose square (n-th power) is x.|x|absolute value / modulus
Distance from zero: |−3| = 3. For a complex number, distance from the origin.iimaginary unit
i² = −1.\log_b xlogarithm, natural log
The exponent b must be raised to for x; ln uses base e.\mathbb{N}number sets
Naturals, integers, rationals, reals, complex numbers.

Làm thế nào: Solve Equations with Fraction or Decimal Coefficients

1. Solve equations with fraction coefficients
2. Solve equations with decimal coefficients
3. Find the least common denominator of
4. Multiply both sides of the equation by that LCD. This clears the fractions.
5. Solve using the General Strategy for Solving Linear Equations.
6. Find the least common denominator of
7. Multiply both sides of the equation by that LCD. This clears the fractions.
8. Solve using the General Strategy for Solving Linear Equations.

Câu hỏi người ta hỏi

What does it mean to solve an equation?

To find every value of the unknown that makes both sides equal. Each step is an operation applied to both sides that keeps the solution set the same, until the unknown stands alone.

Why do I sometimes get two answers?

A quadratic can cross the axis twice, so it can have two solutions. A degree-n polynomial has up to n. The graph shows where each one comes from.

How do I know whether to factor or use the quadratic formula?

Try factoring for a few seconds: look for two numbers that multiply to a·c and add to b. If nothing obvious appears, the discriminant b² − 4ac tells you how many real roots there are, and the formula finds them without guessing.

Một số phần của trang này được chuyển từ OpenStax Prealgebra 2e (CC BY-NC-SA 4.0). Được nén lại và giải thích lại ở đây; lỗi là của chúng tôi.

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