Question

The sum of two numbers is 51 and the difference is 9. What are the numbers?

Answer 1

The numbers are 21 and 30

Answer 2

we dont know what is the two numbers so let us assume that one is x and other is y

so the sum of two numbers will be x+y which is equal to 51

`x+y=51`

and their difference is 9

`x-y=9`

so now we have two equations we can solve this by elimination method.

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we know that we have -y and +y which is same value with opposite sign so we can cancel it and x+x will be 2x and 51+9=60

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we can plug x=30 in any one of the equations

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`x=30, y=21`