GATE Questions and Answers with Explanation

Q:

Pipe A can fill a tank in 16 minutes and pipe B cam empty it in 24 minutes. If both the pipes are opened together after how many minutes should pipe B be closed, so that the tank is filled in 30 minutes ?

A) 21 min	B) 24 min
C) 20 min	D) 22 min

Answer & Explanation Answer: A) 21 min

Explanation:

Let the pipe B be closed after 'K' minutes.

30/16 - K/24 = 1 => K/24 = 30/16 - 1 = 14/16

=> K = 14/16 x 24 = 21 min.

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Filed Under: Pipes and Cistern
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19 13653

Q:

40% of 265 + 35% of 180 = 50% of ?

A) 383	B) 338
C) 84.5	D) 253.5

Answer & Explanation Answer: B) 338

Explanation:

We know that 40% = $\frac{2}{5}$

40% of 265 + 35% of 180 = 50% ?

$\frac{2}{5}$ x 265 + 35% of 180 = 50% ?

We know that (35% of 180 = 180% of 35) & 180% = $\frac{9}{5}$

$\frac{2}{5}$ x 265 + $\frac{9}{5}$ x 35 = 50% ?

106 + 63 = 50% ?

?= 2 x 169 = 338.

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Q:

If $\log_{7} (2)$ = m, then $\log_{49} (28)$ is equal to ?

A) 1/(1+2m)	B) (1+2m)/2
C) 2m/(2m+1)	D) (2m+1)/2m

Answer & Explanation Answer: B) (1+2m)/2

Explanation:

$\log_{49} (28) = \frac{1}{2 \log_{7} (7 \times 4)}$

= $\frac{1}{2} + \frac{1}{2} (2 \log_{7} (2))$
= $\frac{1}{2} + \log_{7} (2)$
= $\frac{1}{2} + m$
= $\frac{1 + 2 m}{2}$ .

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Filed Under: Logarithms
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63 13642

Q:

Which tank will fill first?

which_tank_will_be_first_filled1559193031.jpg image

A) 8	B) 7
C) 10	D) 4

Answer & Explanation Answer: C) 10

Explanation:

From the given diagram,

Tank 10 will be first filled because from tank 1 it will go through tank 4 and tank 10.

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Filed Under: Logic Puzzles
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66 13608

Q:

If 25% of a number is subtracted from a second number, the second number reduces to its four-sixth. What is the ratio of the first number to the second number ?

A) 4:3	B) 2:3
C) 3:2	D) 5:3

Answer & Explanation Answer: A) 4:3

Explanation:

Let the numbers be p & q

q-p/4 = 4q/6

=> q-4q/6 = p/4

=> 2q/6 = p/4

=> p/q = 4/3

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Q:

Jagan went to another town covering 240 km by car moving at 60 kmph. Then he covered 400km by train moving at 100 kmph and then rest 200 km he covered by a bus moving at 50 kmph. The average speed during the whole journey was ?

A) 36 kmph	B) 35 kmph
C) 72 kmph	D) 70 kmph

Answer & Explanation Answer: D) 70 kmph

Explanation:

By car 240 km at 60 kmph
Time taken = 240/60 = 4 hr.

By train 240 km at 60 kmph
Time taken = 400/100 = 4 hr.

By bus 240 km at 60 kmph
Time taken = 200/50 = 4 hr.

So total time = 4 + 4 + 4 = 12 hr.
and total speed = 240+400+200 = 840 km
Average speed of the whole journey = 840/12 = 70 kmph.

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Filed Under: Time and Distance
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9 13475

Q:

A can do a piece of work in 21 days and B in 28 days. Together they started the work and B left after 4 days. In how many days can A alone do the remaining work ?

A) 14 days	B) 18 days
C) 21 deays	D) 16 days

Answer & Explanation Answer: A) 14 days

Explanation:

Let A worked for x days.

x/21 + 4/28 = 1 => x = 18

A worked for 18 days. So, A can complete the remaining work in 18 - 4 = 14 days.

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Filed Under: Time and Work
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Q:

A can write 32 pages in 6 hours and B can write 40 pages in 5 hours. If they write together, in how many hours they can write 110 pages ?

A) 7 hrs	B) 6 hrs 10 min
C) 5 hrs 25min	D) 8 hrs 15 min

Answer & Explanation Answer: D) 8 hrs 15 min

Explanation:

A can write in 1hour = 32/6 pages

Similarly, B in 1 hour = 40/5 pages

Together (A+B) in 1 hour = 32/6 + 40/5 = 40/3

So, A+B write 40/3 pages in 1 hour

A+B write 110 pages in (3/40) x 110 Hours = 8 hours 15 min.

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Filed Under: Time and Work
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