Big Ideas Math: Modeling Real Life, Grade 8
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Big Ideas Math: Modeling Real Life, Grade 8 View details
Chapter Review
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Exercise 23 Page 418

Remember how you can rewrite a repeating decimal as a fraction.

2 pounds

Practice makes perfect

We are told that our friend's cat weighs 0.83 times the weight of our cat and that our friend's cat weighs 10 pounds. We want to know how much more our cat weighs in comparison. We can do this by rewriting 0.83 as a decimal first.

Writing the Repeating Decimal as a Fraction

The first step to find the weight of our cat is by rewriting the given repeating decimal as a fraction. Let's remember how we can write a repeating decimal as a fraction. We will follow five steps.

  1. Assign a variable to represent the repeating decimal.
  2. Write an equation by setting the variable and the decimal equal to each other.
  3. Multiply both sides of the equation by 10^d, where d is the number of repeating digits in the repeating decimal.
  4. Subtract equivalent expressions of the variable and the repeating decimal from each side of the equation.
  5. Solve for the variable. If necessary, write an equivalent fraction so that the numerator and denominator are integers.

Let's do it!

Steps 1 and 2

Let's use the variable x to represent the given repeating decimal number. We can write an equation by setting this variable equal to 0.83.

x=0.83

Step 3

Since the given number has one repeating digit, we will multiply both sides of the equation by 10^1.
x=0.83
x* 10^1=0.83* 10^1
x* 10=0.83* 10
10x=8.3

Step 4

We will now subtract x from both sides of the equation. Since x=0.83, we will substitute 0.83 for x on the right-hand side.
10x=8.3
10x-x=8.3-x
10x-x=8.3- 0.83
9x=7.5

Step 5

Finally, we will solve the equation for x.
9x=7.5
9x/9=7.5/9
9x/9=7.5/9
x=7.5/9
x=75/90
We found that x is equal to 7590. Remember that x is also equal to 0.83. The Transitive Property of Equality tells us that the fraction we got is equal to the given repeating decimal number. x= 0.83 x= 7590 ⇒ 0.83= 75/90

Finding Our Cat's Weight

We found that our friend's cat weighs 7590 times the weight of our cat. From the exercise, we know that our friend's cat weighs 10 pounds. Let's rewrite this as an equation. Let x be the weight of our cat. 75/90 * x = 10 Now let's solve the equation for x to find the weight of our cat.
75/90 * x = 10
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Solve for x
75 * x/90 = 10
75 * x/90 * 90 = 10 * 90
75 * x = 10 * 90
75 * x = 900
75 * x/75 = 900/75
75 * x/75 = 900/75
x = 900/75
x=12
Our cat weighs 12 pounds. Now, we will find how much more our cat weighs by subtracting the weight of our friend's cat from our cat's weight. 12-10 = 2 Therefore, our cat weighs 2 pounds more than our friend's.