Mathmetics

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

Q11.
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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Q12.
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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Q13.
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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Q14.
A boat running downstream covers a distance of 24 kms in 4hrs while for covering the distance upstream it takes 6 hrs. What is the speed of the boat in still water ?
1) 5.5 km/hr 2) 6 km/hr
3) 3.5 km/hr 4) 4.5 km/hr
5)None of these
Answer : None of these
Explanation :  Ans. 5 km/hr
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