eigth grade math help please?

Question

please help me on this problem. math finals are tommorow.

Andy's average driving speed for a 4-hour trip was 45 miles per hour. during the first 3 hours he drove 40 miles per hour. what was his average speed for the last hour of his trip?

please explain to me how to do the problem and also give me the answer. thanks so much!

Answer 1

First, find out the total number of miles traveled by multiplying the average speed (45 miles / hour) by the total time traveled. (4 hours) We obtain 180 miles traveled in total.

Now find the miles he traveled in the first 3 hours by multiplying his speed during those first 3 hours (40 miles / hour) by the time traveled at that speed. (3 hours) We obtain 120 miles traveled in the first 3 hours.

Subtract the distance traveled in the first 3 hours from the total travel distance (180-120) to get the remaining distance Andy had to travel. Divide the remaining distance (60 miles) by Andy's remaining time (1 hour) to obtain his average speed (60 miles / hour) for the remaining time.

Answer 2

at 45 miles per hour for 4 hours (45 x 4) andy drove 180 miles (45 x 4 = 180)
for 3 hours he averaged 40 miles per hour (40 x 3) which means he drove 120 (40 x 3 = 120) miles
that leaves 1 hour to drive the rest of the 180 miles ( 180 - 120) which equals 60 that means he ust have averaged 60 mph that last hour
total miles driven - miles driven in 3 hours = miles driven in last hour (x)
(60 miles in 1 hour = mph)
(45 x 4) - (40 x 3) = x

Answer 3

His speed during the last hour was 60 mph. Here's how you arrive at that answer. If his average speed for the entire 4 hour trip was 45 mph, then the trip was 4 hr x 45 mi/hr = 180 mi long. If during the first three hours he drove 40 mph, then he covered 3 hr x 40 mi/hr = 120 miles during that interval. That means he had to cover 60 miles during the last hour (180 - 120 = 60). So, his average speed during the last hour was 60 mi / 1hr = 60 mph.

Answer 4

45 x 4= 180 - 120 (the first 3 hours) = 60
The average is found by adding each hours speed and then dividing the total by 4, so I just did it backwards.
I'm sure there are other ways, but that is how I did it. : )
Hope this helped. Don't now what kind of math you are focusing on right now.

Good luck on the final!

Answer 5

Well...you can figure out how far he went total by multiplying 4 times 45 to get 180. You can figure out how far he went in 3 hours by multiplying 3 times 40 to get 120. If you subtract the two then you will get 60 miles. So he went 60 miles in one hour. So his speed is...yep, you got it.