Glencoe Math: Course 2, Volume 1
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Glencoe Math: Course 2, Volume 1 View details
9. Direct Variation
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Exercise 15 Page 86

A direct variation is a relationship in which the ratio of y to x is constant.

C

Practice makes perfect

We are asked to determine which of the given relationships represents a direct variation. Let's check each relationship to determine whether the ratio of y to x is constant.

Option A

In option A, we are given the following table.

Hours, x 1 2 3 4
Wages ($ ), y 10 22 36 50

We can calculate the ratio for each value of x by dividing the value of y by the value of x.

Hours, x 1 2 3 4
Wages ($ ), y 10 22 36 50
Ratio 10/1=10 22/2=11 36/3=12 50/4=25/2

A relationship is a direct variation when the ratio of y to x is constant. Since the ratios that we got are not the same, the relationship is not a direct variation.

Option B

Now let's take a look at the table from option B.

Hours, x 1 2 3 4
Wages ($ ), y 10 25 30 50

Like we did before, let's calculate each ratio by dividing the value of y by the value of x.

Hours, x 1 2 3 4
Wages ($ ), y 10 25 30 50
Ratio 10/1=10 25/2 30/3=10 50/4=25/2

In this case, the ratios are not the same, so the relationship is not a direct variation.

Option C

In option C, we are given the following table.

Hours, x 1 2 3 4
Wages ($ ), y 10 20 30 40

Let's find the ratios!

Hours, x 1 2 3 4
Wages ($ ), y 10 20 30 40
Ratio 10/1=10 20/2=10 30/3=10 40/4=10

As we can see, all of the ratios are equal to $10 per hour. This means that the relationship is a direct variation! Let's continue and check option D, just in case.

Option D

Finally, we will consider the table from option D.

Hours, x 1 2 3 4
Wages ($ ), y 6 16 30 48

Let's calculate the ratio for each value of x.

Hours, x 1 2 3 4
Wages ($ ), y 6 16 30 48
Ratio 6/1=6 16/2=8 30/3=10 48/4=12

In this case, the ratios are not the same, which means that the relationship is not a direct variation.

Summary

We found that only the relationship from option C is a direct variation. This means that the correct option is C.