Data Sufficiency 2
Practice and master this topic with our carefully crafted questions.
Each of the questions given below consists of a question followed by three statements. You have to study the question and the statements and decide which of the statement(s) is/are necessary to answer the question.
What is the speed of stream ?
I. The boat covers 24 km in 6 hours moving upstream.
II. The boat covers 24 km in 3 hours moving downstream.
III. The ratio between the speed of boat and stream is 3 : 1 respectively.
I. Speed upstream = 24/6 km/hr = 4 km/hr.
II. Speed downstream = 24/3 km/hr = 8 km/hr.
III. Let the speed of the boat in still water be 3X km/hr.
Then, speed of the stream is X km/hr.
∴ Speed downstream = 2X km/hr,
Speed upstream = X km/hr.
From I and II, we get speed of stream
| = | 1 | (8 - 4) km/hr |
| 2 |
= 2 km/hr.
From II and III , we get 2X = 8
<=> X = 4
Speed downstream = 8 km/hr.
| ∴ Speed of stream = | 1 | (8 - 4) km/hr |
| 2 |
= 2 km/hr.
From I and III, we get X = 4 and 2X = 8.
| ∴ Speed of stream = | 1 | (8 - 4) km/hr |
| 2 |
= 2 km/hr.
Thus, any two of the three will give the answer.
∴ Correct answer is (A)
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.
From I and II
| speed of boat in still water = | 1 | (12 + 4) km/hr |
| 2 |
= 8 km/hr.
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).