Question

If x varies inversaly as y and x=9 when y=21 ,find x when y=7

Answer 1

$x = k \times \frac{1}{y} \\ xy = k \\ 9 \times 21 = k \\ k = 189 \\ xy = 189 \\ x \times 7 = 189 \\ x = \frac{189}{7} = 27$