Data Sufficiency

In a certain group, the average (arithmetic mean) age of the males is 28, and the average age of the females is 30. If there are 100 people in the group, how many of them are males?

(1) The average age of all 100 people is 28.9

(2) There are 10 more males than there are females.


I have a peculiar rather a silly doubt.In the question types of the above kind where it is not mentioned that the group contains only males and females, should we take people who are neither male nor female into account?

no we take only male and female into account.
A) 28m + 30f = 2890
m should be multiple of 5 (as everything else is divisible by 10)
m=5a.
14a + 3f = 289.
also f = 100-5a.
14a + 300 - 15a = 289 a=11, m=55. Sufficient

B) f+10+f=100 f=45,m=55
Sufficient
IMO D

I haven't come across any GMAT problem where they consider the third gender

If you are thinking that the group could include children, then one of the statements should
give you a clue about that

Both statements in this problem are sufficient

Statement 1

M+W=100
28M+30W=2890

Statement 2
M=10+W
M+W=100