Over the Golden Gate

       While in San Francisco some time back, I hired a car to drive over the golden gate bridge. I started in the afternoon when there was no traffic rush. So I could drive at a speed of 40 miles an hour. While returning, however. I got caught in the traffic rush and I could only manage to drive at a speed of 25 miles an hour.

What was my average speed for the round trip?

Answer:  No, the answer is not 32½ miles an hour, though this figure is the obvious answer! However, this represents the average of the 2 speeds and not the average speed for the whole trip.

         If the time is equal to the distance divided by the average speed, then the time for the trip starting from San Francisco equals S/40 and the time for the return trip is ˢ/25 which gives us a total time of s/40+s/25, which equals 13 s/200 which equals 2S times 200/135, which equals 400s/13s or 30- 10/13 miles an hour.

Around the Equator

       Two identical trains, at the equator start travelling round the world in opposite directions. They start together, run at the same speed and are on different tracks.

      Which train will wear out its wheel treads first?

Answer: Naturally, the train travelling against the spin of the earth. This train will wear out its wheels more quickly, because the centrifugal force is less on this train.

Brothers and Sisters

    3 . A family I know has several children. Each boy in this family has as many sisters as brothers but each girl has twice as many brothers as sisters.

      How many brothers and sisters are there?

Answer:   Since the boys have as many brothers as sisters, there must be 1 boy more than the number of girls. If we try 2 and 1, 3 and 2, and 4and 3, we will find that 4 boys and 3 girls is the solution to fulfill the requirement that each girl has twice as many brothers as sisters.

A matter of Time

1.       Fifty minutes ago if it was four times as many minutes past three o’clock, how many minutes is it to six o’ clock?

Answer: Twenty- six minutes.

Tall Men Next Door

Tall Men Next Door 
      

1.       Next door to me live four brothers of different heights. Their average height is 74 inches, and the difference in height amongst the first three men is two inches. The difference between their and the fourth man is six inches.

       Can you tell how tall each brother is?

Answer:  The first brother is 70 inches tall, the second 72, the third 74 and the fourth brother 80 inches tall.