I drove to the beach at a rate of 40 miles per hour. If I had driven at a rate of 30 miles per hour instead, then I would have arrived 20 minutes later. How many miles did I drive?
Guest, it's obviously not 70. Use your brain. And if you math teacher says 70 is the answer then he/she's obviously incompetent.
Let's say x is the time in hours.
Since it would take 20 more minutes, so we have 20/60 = 1/3.
So the distances are equal so
40x = 30(x+ 1/3)
40x = 30x + 10
10x = 10
x = 1
Now let's plug x in. x * 40 = 40 so 40 miles.
40 mph for 40 miles means 1 hour, 30 mph for 40 miles means 1 1/3 hour, and 1 hour is 60 minutes, 1 1/3 hour is 80, 80-60 = 20.
Guest, use your brain.
If you don't understand anything feel free to ask.