Question

The average of 40 numbers is zero out of these the maximum number of positive numbers may be

Answer 1

Average of 40 number is zero.
we know, average = sum of observations/total number of observations
0 = sum of observations/40
sum of observations = 0 × 40 = 0
It means, sum of all 40 numbers must be zero. It is possible only when some among 40 numbers are positive and some are negative .
But question ask , maximum number of positive numbers .
Maximum number of positive numbers = 40 - 1 = 39 .

[ We can assume all numbers except last is positive and sum of all 39 numbers are cancelled by last number . ]