Skip to main content

2016 AMC 10A Problem 12

Problem 12 of 25IntermediateNumber TheoryCounting & Probability

Three distinct integers are selected at random between 11 and 2016,2016, inclusive. Which of the following is a correct statement about the probability pp that the product of the three integers is odd?

Answer choices

Show solution

Solution

The product is odd exactly when all three selected integers are odd. There are 10081008 odd and 10081008 even integers from 11 to 20162016. Because the integers are selected without replacement, p=100820161007201510062014.p=\frac{1008}{2016}\cdot\frac{1007}{2015}\cdot\frac{1006}{2014}. The first factor is 12\frac12, and each of the next two factors is slightly less than 12\frac12. Therefore p<18p<\frac18. Thus, the correct answer is A.

More practice

Concepts: basic probability · parity · sampling without replacement

Problem text and solution from the LIVE past-contest archive. See also the AoPS wiki page for community solutions.