Example 8.87 from Elementary Algebra, 8.9 Use Direct and Inverse Variation

Use Direct and Inverse Variation: example 8.87

When Raoul runs on the treadmill at the gym, the number of calories, c, he burns varies directly with the number of minutes, m, he uses the treadmill. He burned 315 calories when he used the treadmill for 18 minutes.

ⓐ Write the equation that relates c and m.
ⓑ How many calories would he burn if he ran on the treadmill for 25 minutes?

Work it out on paper first. Then open the solution one step at a time, and stop as soon as you can finish on your own.

Your turn

The book's Try It right after this example: same idea, new numbers. Only the answer is given.

The number of calories, c, burned varies directly with the amount of time, t, spent exercising. Arnold burned 312 calories in 65 minutes exercising.

ⓐ Write the equation that relates c and t.
ⓑ How many calories would he burn if he exercises for 90 minutes?

How did it go?

Your turn

The book's Try It right after this example: same idea, new numbers. Only the answer is given.

The number of calories, c, burned varies directly with the amount of time, t, spent exercising. Arnold burned 312 calories in 65 minutes exercising.

ⓐ Write the equation that relates c and t.
ⓑ How many calories would he burn if he exercises for 90 minutes?

	The number of calories, $c$ , varies directly with the number of minutes, $m$ , on the treadmill, and $c = 315$ when $m = 18$ .
Write the formula for direct variation.
We will use $c$ in place of $y$ and $m$ in place of $x$ .
Substitute the given values for the variables.
Solve for the constant of variation.

Write the equation that relates $c$ and $m$ .
Substitute in the constant of variation.

	Find $c$ when $m = 25$ .
Write the equation that relates $c$ and $m$ .
Substitute the given value for $m$ .
Simplify.
	Raoul would burn 437.5 calories if he used the treadmill for 25 minutes.

	The number of calories, $c$ , varies directly with the number of minutes, $m$ , on the treadmill, and $c = 315$ when $m = 18$ .
Write the formula for direct variation.
We will use $c$ in place of $y$ and $m$ in place of $x$ .
Substitute the given values for the variables.
Solve for the constant of variation.

Write the equation that relates $c$ and $m$ .
Substitute in the constant of variation.

	Find $c$ when $m = 25$ .
Write the equation that relates $c$ and $m$ .
Substitute the given value for $m$ .
Simplify.
	Raoul would burn 437.5 calories if he used the treadmill for 25 minutes.

Use Direct and Inverse Variation: example 8.87

Solution

Your turn

Use Direct and Inverse Variation: example 8.87

Solution

Your turn