Important for :

1

2

B

P = ₹ 12000; R = 9%; n = 2 years

CI = | P | ( | 1 + | R | ) |
^{n} |
– P |

100 |

CI = | 12000 | ( | 1 + | 9 | ) |
^{2} |
– 12000 |

100 |

= 12000 × | 109 | × | 109 | – 12000 |

100 | 100 |

= 14257.20 – 12000 = ₹ 2257.20

______________________________________________

To solve this question, we can apply the net% effect formula

Net% effect = | ( | x + y + | xy | ) | % |

100 |

Here, x = y = 9% (because rate of interest is same for both the years)

By the net% effect, we get effective rate of interest

= | ( | 9 + 9 + | 9 × 9 | ) | % = 18.81% | |

100 |

Therefore, 18.81% of 12000 = ₹ 2257.20

Hence, option B is correct.

3

4

D

To solve this question, we can apply a short trick approach

Sum = |
Difference × 100^{2} |

r^{2} |

Given, Difference = ₹ 100, r = 5%

By the short trick approach, we get

Sum = |
100 × 100^{2} |
= ₹ 40000 |

5^{2} |

________________________________________________

We can solve it by the net% formula,

Rate % of SI for 2 yr at 5% pa = 5 × 2 = 10%

Rate % of CI for 2 yr at 5%,

5 + 5 + | 5 × 5 | = 10.25% | |

100 |

% rate difference of CI and SI = 10.25% – 10% = 0.25%

Let the sum be ₹ x, then

0.25% of x = 100

x = | 100 × 100 | = ₹ 40000 |

0.25 |

Hence, option D is correct.

5