Problem 1 :
David drove for 3 hours at a rate of 50 miles per hour, for 2 hours at 60 miles per hour and for 4 hours at a rate of 70 miles per hour. What was his constant-speed for the whole journey?
Problem 2 :
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 constant-speed for the whole journey?
Problem 3 :
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 constant speed for the whole journey if he goes by walking and comes back by riding.
Problem 4 :
David travels from the place A to place B at a certain speed. When he comes back from place B to place A, he increases his speed 2 times. If the constant-speed for the whole journey is 80 miles per hour, find his speed when he travels from the place A to B.
Problem 5 :
Kemka is preparing 20 cups of apple juice in the first 4 minutes and 60 cups in the next 12 minutes. How many cups does she prepare per minute?
1. Answer :
Step 1 :
Formula for constant speed :
= Total distance/Total time taken
Formula for distance :
= Rate x Time
Step 2 :
Distance covered in the first 3 hours :
= 50 x 3
= 150 miles
Distance covered in the next 2 hours :
= 60 x 2
= 120 miles
Distance covered in the last 4 hours
= 70 x 5
= 350 miles
Step 3 :
Then,
total distance = 150 + 120 + 350 = 620 miles
total time = 3 + 2 + 5 = 10 hours
Step 4 :
So, constant speed is
= Total distance/Total time taken
= 620/10
= 62 miles per hour
2. Answer :
Step 1 :
Here, both the ways, he covers the same distance.
Then, formula for constant speed = 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, constant speed is
= 2(45)(55)/(45 + 55)
= 4950/100
= 49.5 miles per hour
3. Answer :
Step 1 :
Walking + Walking = 10 hours -----> walking = 5 hours
Riding + Riding = 8 hours (Because 2 hours gained)
Then, Riding = 4 hours
Walking + Riding -----> ( 5 + 4 ) = 9 hours
Step 2 :
Total time taken = 9 hours
Total distance covered = 18 miles
Step 3 :
So, constant speed is
= Total distance/Total time taken
= 18/9
= 2 miles per hour
4. Answer :
Step 1 :
Let 'a' be the speed from place A to B.
Then, speed from place B to A = 2a
Step 2 :
Here, both the ways, he covers the same distance.
Then, formula for constant speed = 2xy/(x + y)
Step 3 :
x ----> Speed from place A to B
x = a
y ----> Speed from place B to A
y = 2a
Step 4 :
Given : Constant speed = 80 miles/hour
2(a)(2a)/(a + 2a) = 80
4a^{2}/3a = 80
4a/3 = 80
a = 60
Speed from place A to B is 60 miles per hour.
5. Answer :
Step 1 :
Total no. of cups of apple juice prepared is
= 20 + 60
= 80 cups
Step 2 :
Total time taken is
= 4 + 12
= 16 minutes
Step 3 :
Number of cups of apple juice prepared per minute is
= Total number of cups/Total time taken
= 80/16
= 5
Kemka prepares 5 cups of apple juice per minutes.
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