What is the tens digit of the smallest positive integer that is divisible by each of 20, 16, and 2016?
A number or a short expression. Spacing and $ signs are ignored.
Solution
We note that 20=22⋅5 and 16=24 and 2016=16⋅126=25⋅32⋅7. For an integer to be divisible by each of 22⋅5, 24, and 25⋅32⋅7, it must include at least 5 factors of 2, at least 2 factors of 3, at least 1 factor of 5, and at least 1 factor of 7. The smallest such positive integer is 25⋅32⋅51⋅71=10080. The tens digit of this integer is 8.
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