Question

If I varies inversely as r+2, and I=9 when r=3, find r when I=7.
Help please?

Answer 1

The usual formula for inverse variation is

xy = k

In this case,

l = x
y = r + 2

so

l(r+2) = k

which means

9(3+2) = k
9(5) = k
45 = k

Now use the same formula in terms of l and r to find the new value for r given that l = 7.