| Directions: In each of the following questions, a question is followed information given in three statements. You have to study the question along with the statements and decide the information given in which of the statement (s) is necessary to answer the question. |
| What is the average age of 46 students studying in a class? |
| I. The average age of boys is 15.4 yr while the average age of girls is 14.6 yr. |
| II. Boys and girls are respectively in the ratio 4: 5. |
| III. The number of boys is less than that a girls by 5. |
A) I and either II or III
B) I and II
C) I and III
D) All I, II and III
E) None of the above
Correct Answer: A
Solution :
| II. \[\frac{\text{Boy}}{\text{Girl}}=\frac{4}{5}\] |
| \[\therefore \]Number of boys \[=\frac{4}{9}\times 45=20\] |
| Number of girls \[=25\] |
| I. Average age \[=\frac{15.4\times 20+14.6\times 25}{45}\] |
| \[=\frac{308+365}{45}=14.95\,\,\text{yr}\] |
| III. Let the number of girls be \[x.\] |
| \[\therefore \]Number of boys \[=x-5\] |
| \[\therefore \]\[x+x-5=45\]\[\Rightarrow \]\[2x=50\] |
| \[x=25\] |
| Hence, statement I and either II or III will give the solution. |
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