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How many ​two-digit counting numbers are not multiples of 10 ​

User Sunil Purushothaman
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1 Answer

14 votes
14 votes

Answer: 81

Step-by-step explanation:

The two digit counting numbers start at 10 and end at 99.

{10, 11, 12, ..., 98, 99}

There are m = 99-10+1 = 90 items in this list.

The two-digit multiples of 10 are: 10, 20, 30, 40, 50, 60, 70, 80, 90

There are n = 9 items listed here. It might help to think of the set {1,2,3,4,5,6,7,8,9} and tack 0's at the end of each.

So we have m-n = 90-9 = 81 two-digit counting numbers that are not multiples of 10.

User Caleb Gray
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