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A car travels first one-third of a certain distance with a speed of 10 km/hr, the next one-third of the distance with the speed of 20 km/hr and the last one-third distance with a speed of 60 km/hr. The average speed of the car for the whole journey is
- a)18 km/hr
- b)24 km/hr
- c)30 km/hr
- d)36 km/hr
Correct answer is 'A'. Can you explain this answer?
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Verified Answer
A car travels first one-third of a certain distance with a speed of 10...
Let x = total distance.
D=RT and you want to find R (that is, the overall average speed);
where D = Distance, R= rate or speed;
R = D/T
R = x/T [total distance is x]
Now, for each segment, T = D/R for that portion.
R = x / ( (x/3)/10 + (x/3)/20 + (x/3)/60) )[insert the distances and rates]
R = 60x / ( 6(x/3) + 3(x/3) + (x/3) ) [multiply by 1 = 60/60 to get rid of fractions]
R = 60x / (10x/3) [collect terms]
R = 60 * 3/10 [cancel 'x'; to divide by fraction, invert and multiply]
R = 18 km/hr
Most Upvoted Answer
A car travels first one-third of a certain distance with a speed of 10...
Let the total distance be 3x km. Now, average speed is given by
average speed = (total distance travelled) / (total time taken)
So, let times taken for the first, second and third halves of the journeys be t1, t2, and t3 respectively. Then,
t1 = x/10
t2 = x/20
t3 = x/60
So, average speed = x / (t1 + t2 + t3)
= x / (x/10 + x/20 + x/60)
= 3/ ((6 + 3 + 1)/60)
= (3*60)/10
= 18 km/hr
The correct option is A.
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A car travels first one-third of a certain distance with a speed of 10 km/hr, the next one-third of the distance with the speed of 20 km/hr and the last one-third distance with a speed of 60 km/hr. The average speed of the car for the whole journey isa)18 km/hrb)24 km/hrc)30 km/hrd)36 km/hrCorrect answer is 'A'. Can you explain this answer?
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A car travels first one-third of a certain distance with a speed of 10 km/hr, the next one-third of the distance with the speed of 20 km/hr and the last one-third distance with a speed of 60 km/hr. The average speed of the car for the whole journey isa)18 km/hrb)24 km/hrc)30 km/hrd)36 km/hrCorrect answer is 'A'. Can you explain this answer? for Class 9 2024 is part of Class 9 preparation. The Question and answers have been prepared according to the Class 9 exam syllabus. Information about A car travels first one-third of a certain distance with a speed of 10 km/hr, the next one-third of the distance with the speed of 20 km/hr and the last one-third distance with a speed of 60 km/hr. The average speed of the car for the whole journey isa)18 km/hrb)24 km/hrc)30 km/hrd)36 km/hrCorrect answer is 'A'. Can you explain this answer? covers all topics & solutions for Class 9 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A car travels first one-third of a certain distance with a speed of 10 km/hr, the next one-third of the distance with the speed of 20 km/hr and the last one-third distance with a speed of 60 km/hr. The average speed of the car for the whole journey isa)18 km/hrb)24 km/hrc)30 km/hrd)36 km/hrCorrect answer is 'A'. Can you explain this answer?.
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