AVERAGE SPEED PROBLEMS

Problem 1 :

A person travels from New York to Washington at the rate of 45 miles per hour and comes backs to the New York at the rate of 55 miles per hour. What is his average speed for the whole journey?

Answer :

Step 1 :

Here, both the ways, he covers the same distance.

Then, the formula to find average speed is

= 2xy/(x + y)

Step 2 :

x ----> Rate at which he travels from New York to Washington

x = 45

y ----> Rate at which he travels from New York to Washington

y = 55

Step 3 :

So, the average speed is

= (2 ⋅ 45 ⋅ 55)/(45 + 55)

= 4950/100

= 49.5

So, the average speed for the whole journey is 45 miles per hour.

Problem 2 :

A man takes 10 hours to go to a place and come back by walking both the ways. He could have gained 2 hours by riding both the ways. The distance covered in the whole journey is 18 miles. Find the average speed for the whole journey if he goes by walking and comes back by riding.

Answer :

Step 1 :

Given : A man takes 10 hours to go to a place and come back by walking both the ways.

That is,

walking + walking = 10 hours

2 ⋅ walking = 10 hours

walking = 5 hours

Given : He could have gained 2 hours by riding both the ways.

That is,

riding + riding = 8 hours

2 ⋅ riding = 8 hours

riding = 4 hours

Step 2 :

If he goes by walking and comes back by riding, time taken by him :

walking + riding = 5 + 4

walking + riding = 9 hours

Step 3 :

total time taken = 9 hours

total distance covered = 18 miles

Step 4 :

So, the average speed is

= total distance/total time

= 18/9

= 2

So, the required average speed is 2 miles per hour.

Problem 3 :

Lily takes 3 hours to travel from place A to place B at the rate of 60 miles per hour. She takes 2 hours to travel from place B to C with 50% increased speed. Find the average speed from place A to C.

Answer :

Step 1 :

speed (from A to B) = 60 miles/hour

speed (from B to C) = 90 miles/hour (50% increased)

Step 2 :

Formula to find distance is

= rate ⋅ time

Distance from A to B is

= 60 ⋅ 3

= 180 miles

Distance from B to C :

= 90 ⋅ 2

= 180 miles

Total distance traveled  from A to B is

= 180 + 180

= 360 miles

Total time taken from A to B is

= 3 + 2

= 5 hours

Step 3 :

Formula to find average speed is

= total distance/total time

= 360/5

= 72

So, the average speed from place A to B is 72 miles/hour.

Problem 4 :

Distance from A to B = 200 miles

Distance from B to C = 300 miles

Distance from C to D = 540 miles

The speed from B to C is 50% more than A to B. The speed from C to D is 50% more than B to C. If the speed from A to B is 40 miles per hour,  find the average speed from A to D.

Answer :

Step 1 :

speed (from A to B) = 40 miles/hour

speed (from B to C) = 60 miles/hour (50% more)

speed (from C to D) = 90 miles/hour (50% more)

Step 2 :

Formula to find time is

= distance/time

time (A to B) = 200/40 = 5 hours

time (B to C) = 300/60 = 5 hours

time (C to D) = 540/90 = 6 hours

Total time taken from A to D is

= 5 + 5 + 6

= 16 hours

Total distance from A to D is

= 200 + 300 + 540

= 1040 miles

Step 3 :

Formula to find average speed is

= total distance/total time

= 1040/16

= 65

So, the average speed from A to D is 65 miles per hour.

Problem 5 :

Time (A to B) = 3 hours

Time (B to C) = 5 hours

Time (C to D) = 6 hours

If the distances from A to B, B to C and C to D are equal and the speed from A to B is 70 miles per hour, find the average speed from A to D

Answer :

Step 1 :

Formula to find distance is

= rate ⋅ time

Distance from A to B is

= 70 ⋅ 3

= 210 miles

Given : Distance from A to B, B to C and C to D are equal.

Total distance from A to D is

= 210 + 210 + 210

= 630  miles

Total time taken A to D is

= 3 + 5 + 6

= 14 hours

Step 2 :

Formula to find average speed is

= total distance/total time

= 630/14

= 45

So, the average speed from A to D is 45 miles per hour.

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