Answer:
rate boat = 15 mph
rate current = 5 mph
Step-by-step explanation:
d = r * t
t = d/r
240 / (r_boat + current) = 12 Multiply both sides by r_boat + r_current.
240 = 12(r_boat + current)
240/ (r_boat - current) = 24 Multiply both sides by r_boat - r_current
240 = 24*(r_boat - current)
Since the distances are the same in both equations, you can equate the right side of each.
12 (r_boat + current) = 24(r_boat - current) Divide by 12
r_boat + current = 2 (r_boat - current) Remove the brackets.
r_boat + current = 2*r_boat - 2* current add 2 currents to both sides
r_boat + 3currents = 2*r_boat Subtract r_boat both sides
3 currents = r_boat.
240 = 12*(r_boat + current. Divide by 12
20 = r_boat + current Put 3 currents in for r_boat
20 = 3currents + 1 current Combine
20 = 4 currents Divide by 4
5 = current
The rate of the current = 5 miles / hour
3 currents = r_boat
3*5 = rate_boat
15 = rate of the boat