Number system-eighth grade

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Problem: What is the last digit of the product?
61 X 62 X 63 X ...X 69

Solution: From the numbers to be multiplied, we find that one of the numbers, i.e., 65 ends in 5

When 5 is multiplied by an even number, the last digit will be zero.

A number ending in zero multiplied by any other number will give 0 as the last digit of the product.

Hence, zero will be the last digit of the product.