Question

The average of 10 numbers is 13.7. if the average of first five numbers is 12.4 ,and the average of last six numbers is 14.5, what is the 5th number?

Answer 1

Sum of 10 numbers is=13.7*10=137; (n1,n2.....n10)
Sum of last 6 numbers is=6-14.5=87;(n5,n6.....n10)
137-87=50 is the sum of numbers from n1,n2,n3,n4.;
Sum of frist 5 numbers is 12.4*5=62; 
n5=62-50;
n5=12;