Answer: 2.8 mph
Explanation:
First find distance traveled in 4 min by person a.
D=s*t, you get 0.2 miles. So in 4 min, person a traveled 0.2miles.
Distance=3*1/15= 1/5 which equals 0.2 miles.
(t should be in hours since mph, so 4/60, which is simplified tp 1/15)
2. Use concept of relative speed
Remaining distance to person B's house is 3-1/5=14/5 or 2.8 miles. Person A's brother has to cover 2.8 miles faster than person A to catch up.
3. let x = speed in mph the brother must travel to catch up to person A. They are moving in the same direction so relative speed is (x-3) mph, or brothers speed minus person A's speed.
4. Time needed for the brother to catch up to person A = time it takes for Person A to reach person B's house
To find time we can use: Time= Distance/Speed
Person A's brother: Time=14/5 over x
Person A: Time= 3/3=1 hour
Setting these equal to each other gets 14/5 over x=1
5. Solve for x.
Multiply by x to get 14/5.
x= speed the brother needs to travel to catch up, which is 14/5 or 2.8 mph.