In a city, 60% of the population are women, 30% of the women are girls and 40% of the girls have 5-7 years old.
25% of the total of men are boys and 20% of boys have 5-7 years old. There are a total of 2000 5-7 years old boys in the city.
How many 5-7 years old girls are in the city?
Let the population of the city =P
0.3 * 0.6P =0.18P =Girls.
0.4 * 0.18P =0.072P are girls between 5-7 years old.
0.25 * 0.4P =0.1P are boys
0.20 * 0.10P =0.02P are boys between 5-7 years old.
0.02P = 2000
P =2000 / 0.02
P =100,000 People - the population of the city.
0.072 * 100,000 = 7,200 girls between 5-7 years old.