The ratio of roses and lillies in a garden is 3 : 2 respectively. The average number of roses and lillies is 180. What is the number of lillies in the garden?

Let the number of roses and lillies in the garden be 3x and 2x respectively.

According to the question,

$frac{3 x+2 x}{2}=180 Rightarrow frac{5 x}{2}=180$

$Rightarrow x=frac{180 imes 2}{5}=72$

∴ Number of lillies

= 2x = 2 × 72 = 144