+321 Andrew chooses a number from 1 to 100, and Mary also chooses a number from 1 to 100. (They may choose the same number.) It turns out that the product of their numbers is even. In how many ways could Andrew and Mary have chosen their numbers?
+128408 Here's my best attempt
Total possible products = 100 * 100 = 10,000
Look at a simple scenario
Andrew chooses an odd ...... the product is even only if Mary chooses an even number
So......50 even products
Andrew chooses an even .....the product is even no matter what number Mary chooses
So...100 even products
So......we have 50 odds * 50 + 50 evens * 100 = 2500 + 5000 = 7500 even outcomes
