Skip to main content

2015 AMC 10B Problem 10

Problem 10 of 25EasierNumber Theory

What are the sign and units digit of the product of all the odd negative integers strictly greater than −2015?-2015?

Answer choices

Show solution

Solution

There are 10071007 odd numbers greater than −2015.-2015. Our product is of an odd number of negative numbers, so the result is negative. Also, we multiply by −5-5 in there, so the product is a multiple of 5,5, making it end in 55 or 0.0. None of our factors are even, so the product can’t be even. Therefore, the product must end in 5.5. Thus, the correct answer is C .
AoPS wiki

Tagged: units digit · parity

More practice