Important for :

1

2

3

4

B

Let, the number of girls = x & the number of boys = (600 – x)Given, the average age of the boys = 12 years

∴ Total age of the boys = 12(600 – x) years

And, the average age of the girls = 11 years

∴ Total age of the boys = 11x years

Now, average age of the school = | Total age of the boys + Total age of the girls |

600 |

⇒ 11 | 3 | = | 12(600 – x) + 11x |

4 | 600 |

⇒ | 47 | = | 7200 – x |

4 | 600 |

⇒ 7200 – x = 7050

⇒ x = 7200 – 7050 = 150

Hence, option B is correct.

5

B

Price of milk in first year = ₹ 7.50 per litre.∴ Quantity of milk in first year = | 4080 | = 544 litres |

7.50 |

Price of milk in second year = ₹ 8.00 per litre.

∴ Quantity of milk in second year = | 4080 | = 510 litres |

8.00 |

Price of milk in third year = ₹ 8.50 per litre.

∴ Quantity of milk in third year = | 4080 | = 480 litres |

8.50 |

∴ Required average = | 3 × 4080 | = | 12240 | = ₹ 7.98 |

544 + 510 + 480 |
1534 |

Hence, option B is correct.