Precisely one number is removed from the set of positive integers from 1 to n. The average of the remaining numbers is 40.75.
Which integer was removed?
Let x= the number removed.
After removing x from the set the sum is n(n+1)/2 - x
For the average to work out this sum must be 40.75(n-1)
Set these equal and solve for x:
a quick chart reveals the solution:
(You could also solve for n using the quadratic formula and make a chart. The only integer solution is the same as above.)
Posted by Jer
on 2015-06-15 09:12:18