Question

The mean of 10 number is 55, if one number is included,their mean becomes 60. Find the included number.

Answer 1

Mean of 10 numbers = 55
sum of 10 numbers = 550

Now mean of 11 numbers = 60
sum of 11 numbers= 660
The number is 660-550 = 110

Answer 2

Mean of 10 no.s =55
 Let us take y =SUM of those 10 no.s
so y/10=55
so y=550
let us take the unknown no. as x
so y+x/11=60
550+x/11=60
550+x=660
So,x=110