Which number is 100 less than 61 tens?

Well yiu need to find out what is 61 tens so 61 x 10 = 610. 610-100=510

Your answer is 510

Well ... to find 61 tens, just write 61 with the 1 in the tens place then all remaining places to the decimal get a zero (in this case that's just the ones place). So ...

61 tens = 610

100 less than 610 is

610 - 100 = 510