Three whole numbers are each rounded to the nearest 10. The sum of the three rounded numbers is 80. What is the maximum possible sum of the original three numbers?
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1 Answer

The answer is 92.

Let’s see what multiples of 10 add up to 80:

10+10+60, 10+20+50, 10+30+40, 20+20+40, 20+30+30.

Imagine the numbers had all been rounded up:

9+9+59=77, which is less than 80.

But if each number is rounded down to the nearest 10 the maximum ones digit is 4 for each of them, and 3 times 4 is 12, added to 80 is 92:

14+14+64=

14+24+54=

14+34+44=

24+24+44=

24+34+34=92.

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