average of lists

kushal.adhia wrote:The average (arithmetic mean) of the 43 numbers in list L is a positive number. The average of all 48 numbers in both lists L and M is 50 percent greater than the average of the 43 numbers in list L. What percent greater than the average of the numbers in list L is the average of the numbers in list M?


A. 85%
B. 240%
C. 350%
D. 480%
E. 580%

OA is D

I did this one by assuming numbers.
Let the average of 43 numbers be 1
and new average of 48 numbers is 1.5

this means all the 43 numbers has the value 1 and sum of all the values is 43.
and sum of all 48 numbers is 72. 48 * 1.5 = 72

72 - 43 = 29

New 5 Numbers must add up to 29 average of 29/5 = 5.80
Old average is 1
5.80-1 = 4.8

Hope this Helps

thanks for the help guys =)

Kushal

kushal.adhia wrote:The average (arithmetic mean) of the 43 numbers in list L is a positive number. The average of all 48 numbers in both lists L and M is 50 percent greater than the average of the 43 numbers in list L. What percent greater than the average of the numbers in list L is the average of the numbers in list M?


A. 85%
B. 240%
C. 350%
D. 480%
E. 580%

OA is D

Good math solutions (especially the first one - picking numbers is a great way to tackle this type of question), let's take a strategic approach instead.

We know that adding a set of only 5 numbers to a set of 43 numbers increases the average by 50%. So, those 5 numbers must be considerably bigger than the average of the other set: eliminate A and B.

We also know that the question is asking "What percent greater ". Whenever a question asks "what percent greater", there's almost always a wrong answer to punish people for answering the question "what percent of" instead. Now, the difference between "what percent greater" and "what percent of" is exactly 100%. Are there two choices that are 100% apart? Yes!

So, we identify E as the trap answer and D as the correct answer: choose D.

Everything about the GMAT is standardized, including the traps - the better you know how the testmaker thinks, the more you can use that information to your advantage.

Stuart Kovinsky wrote:
We also know that the question is asking "What percent greater ". Whenever a question asks "what percent greater", there's almost always a wrong answer to punish people for answering the question "what percent of" instead. Now, the difference between "what percent greater" and "what percent of" is exactly 100%. Are there two choices that are 100% apart? Yes!

So, we identify E as the trap answer and D as the correct answer: choose D.

Everything about the GMAT is standardized, including the traps - the better you know how the testmaker thinks, the more you can use that information to your advantage.

I will definitely try to use this approach when i m not sure about the answer.
Thanks Sir,
Very well Said,