To solve this we would need to know the number of people who are less than 70 years old, the number of males, and the number of males who are less than 70 years old.

Overlapping sets: quantity of A or B = A + B - (A∩B) = quantity of A + quantity of B - (intersection of A and B)

Number of males = 2500-850 = 1650
Number of people below 70 years old = 2500-800 = 1700
Number of males below 70 years old = 1700-(850*0.4) = 1360

Total number of people who are male OR below 70 = 1650 + 1700 - 1360 = 1990

Probability of male or below 70 = 1990/2500 = 199/250

Answer: B
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Dave de Koos
GMAT aficionado

after solving this problem I learnt two things:
1) Reading the question well enough tells us what to solve for and avoids taking longer routes.
2) If we adopt an accounting approach via something like a double matrix here, it will become more challenging to solve this problem.

The question gives info on Females and population older than 70 years, but asks about a probability of males or younger. Well some arithmetic and probability we need to do.

P(male or <70 yrs) = Prob(male)+Prob(<70)-Prob(male and <70).
let us compute our sample space
n(male) = 2500-850 = 2550-900=1650.
Notice that second part is really number of female and <70 yrs = > 2/5*850= 340.
n of event space = 1650+340 = 1990.
prob = n of event space / number of entire population = 1990/2500 =>199/250.