Question

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

Answer 1

Step-by-step explanation:

Solution :

The mean of 10 numbers is 55

=> the sum of 10 numbers = 55×10 = 550.

When one number is included, the mean becomes 60.

the mean of 11 numbers is 60

=> sum of 11 numbers = 60×11 = 660.

Therefore :

The included number = sum of 11 numbers - sum of 10 numbers

=> 660 - 550

=> 110.

Answer 2

Answer:

Let the sum of 10 numbers be x

So 10x=55

⇒x=550

Let the excluded no. be y

So 9x−y=50

⇒x−y=450

⇒y=550−450

⇒y=100.