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SSC Selection Post 2019 PYQ — Question 63

SSC Selection Post - Matriculation Level 2019 - 15 Oct 2019 • Quantitative Aptitude • Q63

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A person covered 50% of a certain distance at 2 km/h, 25% of the distance at 4 km/h and the remaining distance at 8 km/h. His average speed (inkm / h) for the entire journey was:

 

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Correct answer: C

Explanation

The correct answer is Option 3 i.e. 3211\frac{32}{11}.

Let total distance = D

First 50% , so  D/2 at 2 km/h , so  time = (D/2) ÷ 2 = D/4​

Next 25% , so  D/4​ at 4 km/h , so  time = (D/4) ÷ 4 = D/16​

Last 25% , so  D/4​ at 8 km/h , so  time = (D/4) ÷ 8 = D/32

Total time = D4+D16+D32=11D32\frac{D}{4} + \frac{D}{16} + \frac{D}{32} = \frac{11D}{32}​

Average speed = D11D32=3211\frac{D}{\frac{11D}{32}} = \frac{32}{11}