In a population of grasshoppers, the color green (g) is completely dominant over the color brown (g). if 23% of the population is brown, calculate the percentage of the population that is expected to be heterozygous

The answer is 49.92%

Let's use the Hardy-Weinberg principle:
p + q = 1
p² + 2pq + q² = 1

where:
p - the frequency of dominant allele G
q - the frequency of recessive allele g
p² - the frequency of homozygous dominant individuals GG with colour green
2pq - the frequency of heterozygous individuals Gg with colour green
p² - the frequency of homozygous recessive individuals gg with color brown

23% of the population is brown: p² = 23% = 0.23
p = √(p²) = √0.23 = 0.48

p = 0.48
p + q = 1
0.48 + q = 1
q = 1 - 0.48 = 0.52

The percentage of the population that is expected to be heterozygous is 2pq:
2pq = 2 * p * q = 2 * 0.48 * 0.52 = 0.4992 = 49.92%

They use the si unit, or metric system its all the same thing