Which one of the following pairs is not correctly

Find the unit digit of (57 ¹²⁹  - 7).

Find the average of first 16 whole numbers.

Find the value of 'a' in the given data if the mean of the given data is 16.

10, 12, 18, 20, 15, 17, a, 14, 13, 19

Find the sum of the first 25 natural numbers.

How many digits are required to write first 500 natural numbers?

find the value of 5+55+55+555+…………..+ n terms

The remainder obtained when (47³ + 35³) is divided by 41 is 

Find the unit digit of the expression: 1! + 2! + 3! + 4! + 5! + ........ + 999!.