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**1. 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:**

**A. 8.5 km/hr**

**B. 10 km/hr.**

**C. 12.5 km/hr**

**D. 9 km/hr**

**Answer:** Option B

Explanation:

Man's speed with the current = 15 km/hr

=> speed of the man + speed of the current = 15 km/hr

speed of the current is 2.5 km/hr

Hence, speed of the man = 15 - 2.5 = 12.5 km/hr

man's speed against the current = speed of the man - speed of the current

= 12.5 - 2.5 = 10 km/hr

**2. 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:**

**A. 10**

**B. 6**

**C. 5**

**D. 4**

**Answer: **Option C

Explanation:

Speed of the motor boat =15 km/hr

Let speed of the stream =v

Speed downstream =(15+v) km/hr

Speed upstream =(15−v) km/hr

**3. In one hour, a boat goes 14 km/hr along the stream and 8 km/hr against the stream. The speed of the boat in still water (in km/hr) is:**

**A. 12 km/hr**

**B. 11 km/hr**

**C. 10 km/hr**

**D. 8 km/hr**

**Answer: Option B**

**Explanation:**

Let speed of the boat in still water = a and speed of the stream = b

Then

a + b = 14

a - b = 8

Adding these two equations, we get 2a = 22

=> a = 11

ie, speed of boat in still water = 11 km/hr

**4. A man rows to a place 48 km distant and come back in 14 hours. He finds that he can row 4 km with the stream in the same time as 3 km against the stream. The rate of the stream is:**

**A. 1 km/hr.**

**B. 2 km/hr.**

**C. 1.5 km/hr.**

**D. 2.5 km/hr.**

**Answer: Option A**

Explanation:

Assume that he moves 4 km downstream in x hours

Given that he can row 4 km with the stream in the same time as 3 km against the stream

i.e., speed upstream =3/4 of speed downstream

=> speed upstream = 3x km/hr

He rows to a place 48 km distant and comes back in 14 hours

Now we can use the below formula to find the rate of the stream

Hence, rate of the stream = 1/2(8−6) = 1km/hr

**5. A boatman goes 2 km against the current of the stream in 2 hour and goes 1 km along the current in 20 minutes. How long will it take to go 5 km in stationary water?**

**A. 2 hr 30 min**

**B. 2 hr**

**C. 4 hr**

**D. 1 hr 15 min**

**Answer: **Option A

Explanation:

= 2 hour 30 minutes

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