Synopsis IAS

Answer

Solution

UPSC Prelims

Mathematics

Theme:

Permutation and Combination / क्रमचय और संचय

Q61 2017, Permutation and Combination

How many numbers are there between 99 and 1000 such that the digit 8 occupies the units place?

For 100 to 200: 8 will come at the unit’s place 10 times, i.e. 108, 118, 128…. 198.

Hence, the number of times that 8 will come at unit’s place between 99 and 1000 = 10 × 9 = 90

Q 61. 2017, Permutation and Combination