88.
What is the speed of the boat in still water?
I.
The speed downstream is 12 kmph.
II.
The speed upstream is 4 kmph.
III. In a to and fro journey between two
points, the average speed of the boat was 6 kmph.
A. I and II only
B. All I, II and III
C. III, and either I or II
D. Any two of the three
E. None of these
Answer: Option D
Explanation:
|
From
I and II, speed of boat in still water =
|
1
|
(12
+ 4) km/hr = 8 km/hr.
|
|
2
|
From
II and III, we get:
|
Using
average speed =
|
2xy
|
,
we get:
|
2
x 4 x y
|
=
6
|
|
x + y
|
4
+ y
|
8y =
24 + 6y
y =
12.
|
Required
speed =
|
1
|
(12
+ 4) km/hr = 8 km/hr.
|
|
2
|
Similarly,
I and III also give the answer.
Correct
answer is (D).
