In a population of 1000 individuals, 400 are homozygous  $R{h}^{+ve}\left(DD\right)$, 240 are heterozygous  $R{h}^{+ve}\left(Dd\right)$ and 360 are $R{h}^{-ve}\left(dd\right)$ . The frequency of recessive allele (d) in that population is

Refer XII – NCERT Page No – 137.
In H.W. population, recenive allete frequency calculated by
$q\left(d\right)=\frac{2\times \left(no.ofHomozygousrecessive\right)+No.ofHeterozygousdo\min ant}{2\times \left(Totalno.ofindividuals\right)}$

$q=\frac{2\left(360\right)+240}{2\left(1000\right)}=\frac{960}{2000}$

$q=0.48$