HELP ME I'M LOST!!!!

[sam1313]

help me solve these problems- please explain!!!!

2-3 Direct Variations


28. A 15-minuta long-distance telephone call costs $.90. The cost varies directly as the length of the call. Write an equation that relates the cost to the length of the call. How long is the call that costs $1.32?

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29. The distance a spring stretches varies directly as the amount of weight that is hanging on it. A weight of 2.5 pounds stretches a spring 18 inches. Find the stretch of the spring when a weight of 6.4 pounds is hanging on it .
:?

 

[stapel]

Variation problems translate as follows:

. . . . ."y varies directly with x": y = kx

. . . . ."y varies inversely with x": y = k/x

. . . . ."y varies jointly with x and z": y = kxz

Translate the given information into the appropriate formula. Plug in the given values, and solve for k. Rewrite the equation, inserting this value for k. Then evaluate the equation at the given point.

For instance, in the first example you posted, you would take the appropriate formula, plug in "15" for "x" (being the minutes, the input), plug in "0.9" for "y" (being the cost, the output), and solve for the value of k. Then you would rewrite the equation, using this value of k, and evaluate at y = 1.32, solving for the value of x, being the minutes that generated that cost.

For further information, please review the following:

. . . . .FreeMathHelp lesson: Direct Variation

Eliz.