Question

How many minutes he does arm routine and abdominal routine

Answer 1

Let
`x` be the amount of time it takes to perform an arm routine and
`y` be the amount of time it takes to perform an abdominal routine. We see:


`4x+y=70`

`4x+2y=100`

Subtracting the second equation from the first gives
`y=30`. Substituting gives
`4x+30=70`, so
`4x=40` and
`x=10`.

Thus, an arm routine takes ten minutes and an abdominal routine takes thirty minutes.