Question

If y varies directly as x, and y is 18 when x is 5, which expression can be used to find the value of y when x is 11?

Answer 1

solution

yαx

⇒y=kx

18=k(5)

⇒k=18/5

then

y=kx

⇒y=(18/5)*11

y=198/5

Answer 2

Direct variation :  

Two quantities are said to vary directly if the ratio of their values remains constant.

If y varies directly to x

y/x= constant

y /x = k (constant)

The Direct Variation Formula :

y = kx  

SOLUTION :  

Given :  

y = 18 , x = 5

Find k with this values  

y = kx  

18 = k × 5

k = 18/5

x = 11 (Given)

Find y with k = 18/5 & x = 11

y = kx  

y = (18/5) × 11

y = 198/5

Hence, the value of y is 198/5

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