graduating - male & female

[Xbond]

Hi there,

I didn't understand why the right answer is B; I used the matrix method but I failed. Could you explain to me how to resolve ?

If the graduating class of certain college, 48% of students are male and 52% are female. In this class, 40% of the Male & 20% of the female student are 25 years old or older. If one student in the graduating class is randomly selected approximately what is the probability that he or she will be less than 25 years old ?

a) 0.90
b) 0.70
c) 0.45
d) 0.30
e) 0.25

[salar_snake]

Suppose you have a 1000 students:

480 are males, 520 are females.

60% of males + 80% of female = number of student under 25 years old.

so 0.6(480) + 0.8(520) = 288 + 416 = 704

the probability = 704/1000

[Xbond]

many thks