BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Average age

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 165
Joined: Wed Mar 24, 2010 8:02 am
Thanked: 2 times
Followed by:1 members

Average age

by HPengineer » Sat Oct 02, 2010 6:14 pm
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.



How to use weighted average to solve?
Top
Source: — Data Sufficiency |
Master | Next Rank: 500 Posts
Posts: 265
Joined: Mon Dec 28, 2009 9:45 pm
Thanked: 26 times
Followed by:2 members
GMAT Score:760

by mj78ind » Sat Oct 02, 2010 6:21 pm
HPengineer wrote: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.



How to use weighted average to solve?
One cool trick is we don't have to solve it but ensure that it can be solved and only one value will result.

1 - 28.9 = {28*x + 30*(100-x)}/100 will give us a unique x, which is the number of men

2 - x + x+ 10 = 100. x+10 is the number of males can solve

Hence D
Call me 1 - (412) 897 6727 (US) or leave a msg on BTG for GMAT advise / questions.
If you like the solution, check out my debrief at and leave a comment:
https://www.beatthegmat.com/760-done-dea ... 66740.html
Top
Master | Next Rank: 500 Posts
Posts: 165
Joined: Wed Mar 24, 2010 8:02 am
Thanked: 2 times
Followed by:1 members

by HPengineer » Sat Oct 02, 2010 6:31 pm
cool i was on the right track!! good to know thanks!
Top
Post new topic Post Reply
• Page 1 of 1