Question

A first number plus twice a second number is 21. Twice the first number plus the second totals 15. Find the numbers.

Answer 1

The first number is equivalent to 3

The second number is equivalent to 9

Explanation:

`n_(1)+2n_(2) =21\\2n_(1) +n_(2) =15\\\\2n_(1) +n_(2) =15\\2(2n_(1) +n_(2)) =(15)2\\4n_(1) +2n_(2) =30\\2n_(2)=-4n_(1)+30` Now, plug this equation in to the first equation

`n_(1)+2n_(2)=21\\n_(1)-4n_(1)+30=21\\-3n_(1)=-9\\n_(1)=3` Now, plug this number in to either equation

`2n_(1)+n_(2)=15\\2(3)+n_(2)=15\\6+n_(2)=15\\n_(2)=9`