Question

Use elimination to solve: NN+ND=50
5NN+10ND=450

Answer 1

`5NN+10ND=450\\5(NN+2ND)=450 \\ NN+2ND=90 \\ \\ \boxed{NN=90-2ND} \\ \\ NN+ND=50 =>\boxed{NN=50-ND} \\ \\ \\ 90-2ND=50-ND \\ -2ND+ND=50-90 \\ -ND=-40 \\ \\ \boxed{ND=40} \\ \\ NN=50-ND \\ NN=50-40 \\ \\ \boxed{NN=10}`