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# 中三maths (複利息)

題目是 :

Jack broorws HK$1,000.00. He only gets HK$900.00 and he has to repay HK$1,300 in two weeks. If no money is repaid after two weeks. HK$1,300 will be taken as the principal and the interest will be calculated as the same interest rate [Assuming there are 52 weeks in a year]

a) Find the interest for the first two weeks ANSWER : HK$400(這個我明白)

b) Find the yearly interest rate for the first two weeks ANSWER : 1155.6%(這個不明白)

c) If no money is repaid for teh first two weeks. find the total interest after the first four weeks. ANSWER : HK$977.80 (這個不明白)

### 2 Answers

- 翻雷滾天 風卷殘雲Lv 79 years agoFavorite Answer
b) Since the interest is $400 for 2 weeks, the interest rate for 2 weeks is 400/900 x 100% = 44.44%

Hence the interest rate for a year will be 44.44 x 26 = 1156 % since in a year there are 26 times of 2 weeks.

c) After the first 4 weeks, the amount will be 1300 x (1 + 44.44%) = $1877.8

Hence interest = 1877.8 - 900 = 977.8

2011-11-03 08:39:47 補充：

為什麼本金是900, 而不是1,000呢??

因為借錢者實際得 900, 不是 1000

為什麼是44.44 X 26而不是44.44的26次方呢??複利息不是用次方計的嗎?我想是因為"the yearly interest rate for the first two weeks"

因為年利率 = per annum, 即是將一年的率攤分若干週期. 題目中所說到的年利率是指若以 simple int. 計的話會是多少.

Source(s): 原創答案 - Anonymous9 years ago
厲害喔!! 謝謝耐心解答...感激感激!!! ^_^