10. Problem number 10. What is the units digit of the product 5 to the power of 5 plus 1 times 5 to the power of 10 plus 1 times 5 to the power of 15 plus 1? The units digit of any integer 5 to the power of n where n is a positive integer is 5. So the units digit of 5 to the power of 5 plus 1, 5 to the power of 10 plus 1, and 5 to the power of 15 plus 1 are all equal to 6 because 5 to the power of 5, 5 to the power of 10, and 5 to the power of 15 all have a units digit of 5 and you add 1 to that to get the units digit of 6. The units digit of their product is the units digit of 6 times 6 times 6 equals 216, which is 6. So the correct answer is E.

units digit

power of 5

integer

product

mathematics