+57 Starting at home, Ishaan traveled uphill to the grocery store for 12 minutes at just 15 mph. He then traveled back home along the same path downhill at a speed of 30 mph.
What is his average speed for the entire trip from home to the grocery store and back?
+9479 His average speed will be the total distance he traveled divided by the total amount of time it took him.
Find his total distance:
12 minutes is 12/60 hours, or 0.2 hours.
He went 15 mph for 0.2 hours, so the distance to the grocery store is 15(0.2) = 3 miles.
He went to the grocery store and back twice so his total distance was 3(2) = 6 miles.
Find his total time:
The first trip was 12 minutes.
He went twice as fast on the second trip so his time will be half as much. 12/2 = 6 minutes.
His total time is 12 + 6 = 18 minutes.
Average speed = 6 miles / 18 minutes
Average speed = 1/3 miles per minute.
Average speed = 20 miles per hour.
+118667 Very nicely explained hectictar 
I'd give you more points if I could. Hopefully Athena will give you some points (stars) too :))
+37159 Here is another gander
r x t = d
a) 12 x 15 = d
b) 6 x 30 = d
a+b = total distance AND (a+b) / time = rate [(12 x 15) +( 6 x30) ] / 18 = 20mph
