Question

Two planes which are 3720 miles apart, fly toward each other. Their speeds differ by 30 mph. If they pass each other in 4 hours, what is the speed of each?

Answer 1

`480 mph and 450 mph`

Explanation:

let say thier speed are `v_1` and `v_2` respectively.
therefore,
`v_1 - v_2 = 30 ->i` and

`v_1 t + v_2 t = 3720`

`t( v_1 + v_2) = 3720`

since `t = 4`,
`v_1 + v_2 = 3720/4 = 930 ->ii`

we can find `v_1` and `v_2` by solving silmutaneos equations `i` and `ii`

let say we use eliminate method `(i + ii)`
`2 v_1 = 960`

`v_1 = 960/2 = 480` mph

replace `v_1 = 480` into `i`,

`480 - v_2 = 30`

`v_2 = 450` mph