How many 4 digit numbers have 6 as their second digit?

Answer 1

There are 9 digits that can be the first digit (1-9);

for each of these there is 1 digit that can be the second digit (6);

for each of these there are 10 digits that can be the third digit (0-9);

for each of these there are 10 digits that can be the fourth digit (0-9).

→ number of numbers is 9 × 1 × 10 × 10 = 900 such numbers.

Answer 2

There are 900 such numbers.