Hint: Remember that Time = Distance ÷ Speed, and Speed = Distance ÷ Time.
Answer: 48 miles per hour.
Time = Distance ÷ Speed
Speed = Distance ÷ Time
The outward journey took 174 miles ÷ 40 mph = 4.35 hours.
The return journey took 174 miles ÷ 60 mph = 2.9 hours.
So I travelled a total of 2 x 174 = 348 miles. I did this in a total of 4.35 + 2.9 = 7.25 hours.
My overall average speed was therefore 348 miles ÷ 7.25 hours = 48 miles per hour. QED.
You are given a 10x10x10 cube composed of one thousand 1x1x1 mini-cubes glued together.
If you removed the outermost layer, how many mini-cubes would you have removed?
Hint: Think about one face at a time.
You started with 10x10x10 = 1000 cubes.
Removing the outermost layer would leave a 8x8x8 large cube = 512 cubes.
Therefore you would have removed 488 cubes (1000 - 512 = 488).