Question

the arithmetic mean of 6numbers is 15 on adding 7th number the mean become 14find 7th number

Answer 1

∑x6/6 = 15 or, ∑x6 = 90

∑x7/7 = 14 or, ∑x7 = 98

the last number is (98-90) = 8

Answer 2

8

a1, a2, .............., a6 be 6 numbers.

a1 + a2 +...........+a6 ÷6=15

a1 +a2 +.........+a6 =15*6

                            = 90

a1+a2+........+a6+a7÷7= 14

                i.e, 90 + a7 = 14 *7 =98

∴ a7 = 98-90 =