**If Nishu can swim downstream at 6kmph and upstream at 2kmph.What is his**

speed in still water ?

A.5 km/hr

B.4 km/hr

C.8km/hr

D.7km/hr

Answer

Option (b) is correct

**Explanation:**

Given : speed downstream a = 6 kmph

Speed upstream b = 2kmph

Speed in still water = (a+b)/2 kmph

= ½ (6+2)

= 8/2 = 4kmph

speed in still water = 4kmph

**Ashok can row upstream at 8kmph and downstream at 12kmph.What is the ****speed of the stream ?**

A.6km/hr

B.3km/h

C.2 km/hr

D.4km/hr

Answer

Option (c) is correct

**Explanation:**

Speed downstream a = 12kmph

Speed upstream b = 8 kmph

Speed of the stream = ½ (a-b) = ½ (12-8)

= 4/2 = 2 kmph

speed of the stream = 2kmph

**A man rows 750m in 775 seconds against the stream and returns in 7 (****1/2) minutes. What is rowing speed in still water ?**

A.4.7km/hr

B. 4km/hr

C.3.5km/hr

D.6km/hr

Answer

Option (a) is correct

**Explanation:**

Speed upstream ‘b’ = 750m / 775 sec = 30/31 m/sec

Speed downstream ‘a’ = 750 m/ (15/2)minutes, a = 750m/450 sec =5/3 m/sec

speed in still water = ½ (a+b)

= ½ (750/450 + 750/675 ) m /sec

= ½ (750/450 + 750/675 ) x 18/5 km/hr

= ½ (5/3 + 30/31) x 18/5 km/hr

= 4.7 km/hr

**A man can row 9 (1/3) kmph in still water and finds that it takes him ****thrice as much time to row up than as to row down the same distance in the river. What is speed of the current ?**

A. 5km/hr

B.3(1/2) km/hr

C.4 (2/3) km/hr

D.8 (3/2)km/hr

Answer

Option (c) is correct

**Explanation:**

Let man’s rate upstream be x km/hr.

Then his rate downstream is 3 x km/hr

Given:

Speed in still water = 9 (1/3) = 28/3 km/hr

i.e, ½ (a+b) = 28/3 km/hr

½ (x+3x) = 28/3

2x = 28/3 x = 28/ 2 x 3 = 14/3 km/hr

rate upstream b = 14/3 km/hr and

rate downstream a = 14/3 x 3 = 14 km/hr

speed of the current = ½ (a-b) = ½ (14 – 14/3)

= ½ (42-14/3) = 28/6 = 4 (2/3) km/hr

**Sham can row a boat at 10kmph in still water. IF the speed of the ****stream is 6kmph, the time taken to row a distance of 80km down the stream is**

A.4 hours

B.5hours

C.3 hours

D.2 hours

Answer

Option (b) is correct

**Explanation:**

Given:

Speed in still water, ½ (a+b) = 10 km/hr

a+b = 20 km/hr…………….(1)

speed of the stream, ½ (a-b) = 6km/hr

a-b = 12 km/hr …………….(2)

(1)+(2 ) we get 2a = 32

a = 16 km/hr

speed downstream =distance traveled / time taken

time taken = 80/16 = 5 hours

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