when average age of 21 members are 0 , how many members greater than 0 ?
"average of 21 numbers = 0 . sum of 21 numbers ( 0 x 21 ) = 0 . it is quite possible that 20 of these numbers may be positive and if their sum is a then 21 st number is ( - a ) answer is 20 ( b )"
subtract(21, const_1)