Question

a coast guard ship left the port at 30 mph. four hours later a helicopter was dispatched at 90 mph to intercept the ship. how long will it take the helicopter to catch the ship?

Answer 1

Make a chart for the pieces of RT=D that you know.

Rate X Time = Distance
_____________________________________
ship 30 x 30x
chopper 90 x-4 90(x-4)

You know that at the time the helicopter overtakes the ship that the distances are equal.

30x=90(x-4) set distances equal
30x = 90x-360 ditribute
-60x = -360 subt 90xfrom both sides
x =6 divide by -60

x-4 is the helicopter's time so plug in
6 for x

6-4 = 2

therefore the helicopter will take over
in 2 hours.