If y varies directly with x, and y = V 49 when x = V196, what is y when x = V100 ?

y  =  −  4.98

Explanation:

This statement means  y  ∝  x , which can also be written in the form  y  =  k x  when it is directly proportionate and  y  =  k  x  when inversely proportionate, where  k  is a value we need to work out.

Since the equation is in the form  y  =  k  x  we know that...  21  =  K  ×  7  

∴  k =  21 /7  =  3 .

So we can write this as the formula:  y  =  3 x

Therefore using the value of  x  =  −  1.66

y  =  3 x  →  y  =  3  ×  −  1.66  =  −  4.98

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