1.

If 3x+2y=15 and x +y=10, what is the value of y ?

Answer»

`-15`
`-5`
5
15

Solution :Isolate x in the second equation, then substitute the result into the first equation:
`x =10-y`
` 3 (10-y)+2y=15`
`30-3y+2y=15`
` -y =-15`
`y =15`
If you NEEDED to KNOW the value of x as well, you COULD now substitute 15 for y into either equation to FIND that `c =-5.` The correct answer is (D).


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