Bunuel wrote:

30 students had an average of X, while 20 students had an average of 80. What is the average for the entire group?

(A) (X + 80)/50

(B) (X + 80)/2

(C) 50/(X + 80)

(D) 3X/5 + 32

(E) (30X + 80)/50

Instead of calculating, we'll pick an easy number for X.

This is an Alternative appraoch.

Say X = 80.

Then all students had an average of 80 so the total average must also be 80.

(A) is not 80.

(B) is 80. Maybe. Let's check the others.

(C) is not 80.

(D) is 240/5 + 32 = 48 + 32 = 80.

(E) is (3*80+8)/5 = 248/5 which is not 80.

So our answer is (B) or (D).

Let's now try X = 0. Then the average is (20*80)/50 = 160/5 = 32

(B) is 40. No!

(D) is 0 + 32 = 32 and is our answer.

(D) is our answer.

_________________

David

Senior tutor at examPAL

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