Question

mean of 9 no is 50 if one no is included their mean becomes 55. Find the included no

Answer 1

let sum of 9 numbers = x
let number included = y
according to question...
mean of 9 numbers = 50
sum of 9 numbers / 9 = 50
x / 9 = 50
x = 50 * 9
x = 450
now mean of 10 numbers (including new number) = (sum of 9 numbers + y) / 10
55 = ( 450 + y ) / 10
550 - 450 = y
y = 100
so the included number is 100