The sum of three numbers $a, b$ and $c$ is 60. If we decrease $a$ by 7, we get the value $N$. If we increase $b$ by 7, we get the value $N$. If we multiply $c$ by 7, we also get the value $N$. What is the value of $N$?
a + b + c = 60
N = a - 7 ⇒ N + 7 = a
N = b + 7 ⇒ N - 7 =b
N = 7c ⇒ N / 7 = c
So
(N - 7) + ( N + 7) + N /7 = 60
2N + N /7 = 60 multiply through by 7
14N + N = 420
15N = 420
N = 420 / 15 = 28
Thank you!
