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Let A equal the number of four digit odd numbers. Let B equal the number of four digit multiples of 3. Find  A + B.

 Oct 17, 2020
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How many 4-digit numbers are there? Well, you have:9,999 - 1,000 + 1 =9,000 such numbers. How many of them are odd? Half of them, or: 9,000 / 2 =4,500 odd integers. How many of them are multiples of 3? 9,000 / 3 =3,000. So A + B =4,500 + 3,000 =7,500. And that is it.

 
 Oct 17, 2020
edited by Guest  Oct 17, 2020

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