Mathmetics

ISBT Mathmetics for all banking PO,Clerk,IBPS PO,Railway,SSC,IAS,OAS Exams

Q521.
A man takes twice as long to row a distance against the stream as to row the same distance in favour of the stream. The ratio of the speed of the boat (in still water) and the stream is:
1) 2:1 2) 3:2
3) 2:3 4) 3:1
5)None of these
Answer : 3:1
Explanation :

Let man's rate upstream be x kmph.

Then, his rate downstream = 2x kmph.

 (Speed in still water) : (Speed of stream) = (2x+2) /2 : (2x-x)/2

   =3x/2: x/2 = 3 : 1.

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Q522.
A boat covers a certain distance downstream in 1 hour, while it comes back in 1 hours. If the speed of the stream be 3 kmph, what is the speed of the boat in still water ?
1) 10kmph 2) 12kmph
3) 15kmph 4) 18kmph
5)None of these
Answer : 15kmph
Explanation :

Let the speed of the boat in still water be x kmph.  Then,

Speed downstream = (x + 3) kmph,

Speed upstream = (x - 3) kmph.

 (x + 3) x 1 = (x - 3)/2 x3

Or 2x + 6 = 3x - 9

Or  x = 15 kmph.

 

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Q523.
A man can row at 5 kmph in still water. If the velocity of current is 1 kmph and it takes him 1 hour to row to a place and come back, how far is the place ?
1) 2.4 km 2) 2.5km
3) 3km 4) 3.6km
Answer : 2.4 km
Explanation :

Speed downstream = (5 + 1) kmph = 6 kmph.

Speed upstream = (5 - 1) kmph = 4 kmph.

Let the required distance be x km.

Then,x/6 +x/4 = 1

 Or  2x + 3x = 12

Or  5x = 12

Or  x = 2.4 km.

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Q524.
A motorboat, whose speed in 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km/hr) is:

1) 4 2) 5
3) 6 4) 10
5)None of these
Answer : 5
Explanation :



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Q525.
A man's speed with the current is 15 km/hr and the speed of the current is 2.5 km/hr. The man's speed against the current is:
1) 7.5 km/hr 2) 8.5 km/hr
3) 10 km/hr 4) 12.5 km/hr
5)None of these
Answer : 10 km/hr
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Q526.
n one hour, a boat goes 11 km/hr along the stream and 5 km/hr against the stream. The speed of the boat in still water (in km/hr) is:
1) 3 km/hr 2) 5 km/hr
3) 8 km/hr 4) 9 km/hr
5)None of these
Answer : 8 km/hr
Explanation : Speed in still water = ½(11 + 5) kmph = 8 kmph.
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Q527.
A man's speed with the current is 15 km/hr and the speed of the current is 2.5 km/hr. The man's speed against the current is:
1) 8.5 km/hr 2) 9 km/hr
3) 10 km/hr 4) 12.5 km/hr
5)None of these
Answer : 10 km/hr
Explanation :
Man's rate in still water = (15 - 2.5) km/hr = 12.5 km/hr.
Man's rate against the current = (12.5 - 2.5) km/hr = 10 km/hr.
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Q528.
A boat can travel with a speed of 13 km/hr in still water. If the speed of the stream is 4 km/hr, find the time taken by the boat to go 68 km downstream.
1) 2 hours 2) 3 hours
3) 4 hours 4) 5 hours
5)None of these
Answer : 4 hours
Explanation :
Speed downstream = (13 + 4) km/hr = 17 km/hr.
Time taken to travel 68 km downstream = ( 68/17) hrs = 4 hrs.
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Q529.
In a stream that is running at 2 km/hr , a man goes 10 km upstream and comes back to the starting point in 55 min. Find the speed of the man in still water  ?
1) 20 km/hr 2) 22 km/hr
3) 24 km/hr 4) 28 km/hr
5)None of these
Answer : 22 km/hr
Explanation :
Let the speed of the man in still water be x km/hr. then,
 km/hr.
        10/(x-2) + 10/(x+2) = 55/60
        or  x = 22 km/hr
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Q530.
The average weight of A, B and C is 45 kg. If the average weight of A and B be 40 kg and that of B and C be 43 kg, then the weight of B is:
1) 17 kg 2) 20 kg
3) 26 kg 4) 31 kg
5)None of these
Answer : 31 kg
Explanation :
Let A, B, C represent their respective weights. Then, we have:
A + B + C = (45 x 3) = 135 .... (i)
A + B = (40 x 2) = 80 .... (ii)
B + C = (43 x 2) = 86 ....(iii)
Adding (ii) and (iii), we get: A + 2B + C = 166 .... (iv)
Subtracting (i) from (iv), we get : B = 31.
B's weight = 31 kg.
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