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A direct variation is a relationship in which the ratio of y to x is constant.
C
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.
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.
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.
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 $10 per hour. This means that the relationship is a direct variation! Let's continue and check option D, just in case.
Finally, we will consider the table from option D.
| Hours, x | 1 | 2 | 3 | 4 |
|---|---|---|---|---|
| Wages ($ ), 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.
We found that only the relationship from option C is a direct variation. This means that the correct option is C.