Q2 AVERAGES
A set of consecutive positive integers beginning with 1 is written on the blackboard. A student came along and erased one number. The average of the remaining numbers is 35( 7/17 ). What was the number erased?
a. 7
b. 8
c. 9
d. None of these
A better and easier method is as
follows:
First of all, when ever a number is deleted from consecutive numbers, avg
cant change more than 1/2.
So in this case new avg
is 35 7/17, so old average was 35.
Now, 7/17 = 28/68 . So effectively, the number which was deleted gave 28/68 to each 68 num left, so the number should have been 28 less than 35(old avg)
Ans= 35-28=7
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Video Explanation
