Agardener plants 200 flowering plants of the same species. 98 plants have white (v) flowers and the remaining have violet (v) flowers. what must be the allelic frequency of each type of flower? ( p + q = 1, p2 + 2pq + q2 = 1)

The answer is 0.3 (violet flower allelic frequency) and 0.7 (white flower allelic frequency) 

Alleles are different forms of a gene. There can be recessive alleles (v) and dominant alleles (V) that can mask recessive alleles when found together. Allelic frequencies are:
p for dominant allele V
q for recessive allele v

Genotypes can be:
VV - dominant homozygote with violet flowers and with frequency p²
Vv - heterozygote with violet flowers and with frequency 2pq
vv - recessive homozygote with white flowers and with frequency q²

It is given 98 flowers out of 200 are white with frequency q²:
q² = 98/200 = 0.49

From here, we can calculate the frequency of recessive allele v:
q = √q² = √0.49 = 0.7

Since we know q, using the formula p + q = 1, we can calculate the frequency of dominant allele V is:
p + 0.7 = 1
⇒ p = 1 - 0.7 = 0.3