Question

How do you find `f(20)`, if `f(x)` varies inversely with `x` and `f(12)=5`?

Answer 1

`f(20)=3`

Explanation:

As `f(x)` varies inversely as `x`, we have `f(x)=k*1/x`

and as `f(12)=5`, we have `k*1/12=5` i.e. `k=12xx5=60`

Hence `f(x)=60*1/x=60/x`

and `f(20)=60/20=3`