It is the unit's digit of the product of the unit's digits.
For example, the units digit of 123456 * 4689
is simply the units digit of 6*9 = 54, which is 4.
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When multiplying numbers with the same units digit, the units digit of the product is determined by the units digit of the base number raised to the power of the number of times it is being multiplied. In this case, since 7 is being multiplied 100 times, the units digit of the product will be the same as the units digit of 7^100. The units digit of 7^100 can be found by looking for a pattern in the units digits of powers of 7: 7^1 = 7, 7^2 = 49, 7^3 = 343, 7^4 = 2401, and so on. The pattern repeats every 4 powers, so the units digit of 7^100 will be the same as 7^4, which is 1. Therefore, the units digit of the product when one hundred 7's are multiplied is 1.
Find the units digit of 8*7. The 30 in 38 will have no effect on the units digit.
84.42 or 42.21
For any integer greater than 5, where the units digit is 5 then that number can be expressed as the product of n and 5. As such, the number is composite. Therefore all numbers in the range 150 to 200 that have a units digit of 5 are composite,.
Power 2: units digit 9. Multiply by 49 again to get power 4: units digit 1. So every 4th power gives units digit 1. So 16th power has units digit 1, so the previous power, the 15th must have units digit 3.