Answer :

Solution :

In four-digit integer, the digit group "37" (in the same sequence) appears as given below.

Case 1: _ _ 3 7

In this case, 37 appears once in each hundred i.e. Once in 1101 to 1199 (1137) and Once in 1201 to 1299 (1237) … There are 90 such instances from 1001 to 9999.

Case 2: _ 3 7 _ In this case, 37 appears 10 times in each thousand i.e. 10 times in 1101 to 1999 (1370 to 1379) and Once in 2101 to 2999 (2370 to 2379) … There are 9 such instances from 1001 to 9999. Total number of times that 37 have appeared = 10 × 9 = 90

Case 3: 3 7 _ _ In this case, 37 appears 100 times i.e. from 3700 to 3799

Therefore, total number of times the digit group "37" appears = 100 + 90 + 90 = 280