if x varies inversely as y, and x is 20 when y is 9, find y when x is 15

Question

need to find y when x is 15

Answer 1

Hi Kalina, if x varies inversely as y, the first step is to find the proportionally constant k.

 

x = k / y

 

Given: x = 20, y = 9

 

Find k:

 

20 = k / 9

 

k = 180

 

Find y:

 

x = k / y

 

y = k / x

 

y = 180 / 15

 

y = 12

 

When x goes down, y goes up.

 

Answer: y = 12

 

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