CAT 2017 Quantitative Ability

Question : 10 of 34

Marks: +1, -0

A bus travels from City A to City B at a constant speed. If the speed of the bus increases by 8 km/h, it will reach its destination 3 hours earlier. On the contrary, it the speed decreases by 4 km/h, then the bus will reach the destination 8 hours later than the scheduled time. Approximately, how long does the bus usually take?

$5 4/13$
$7 5/13$
$5 7/13$
$5 7/11$

Validate

Solution:

Let the normal speed be S and normal time taken by T hours.
Then, (S + 8)(T- 3) = ST ...(i)
and (S - 4) (7 + 8) = ST ...(ii)
Solving equation (i) and (ii),
we get 8T - 3S = 24
and 8S - 47 = 32
Solving for T, we get T =

\;\;{72}/{13}hr=5\;\;{7}/{13}h

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