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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?

 Mar 31, 2021
 #1
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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

 

cool cool cool

 Mar 31, 2021

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