Counting again

Probability Level 2

How many three digit positive numbers are there for which the units digit is equal to the tens digit? (Don't count, there is a method to solve this problem)


The answer is 90.

Hana Wehbi by Hana Wehbi , 51, USA

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1 solution

Zee Ell
Jul 3, 2017

We can choose the first digit 9 ways (1 to 9) and the second digit (= 3rd, so there is 1 choice left for the third digit) 10 ways (0 to 9).

Hence, our answer should be:

9 × 10 × 1 = 90 9 × 10 × 1 = \boxed {90}

3 Helpful 0 Interesting 0 Brilliant 0 Confused

Yes, you are correct. Thank you.

Hana Wehbi - 3 years, 11 months ago

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