英文數學!!20分 - Ans.fyi 參考答案

英文數學!!20分

2012-08-14 9:30 am

1,A computer game software marked at$280 is sold at 20% off. If the discount is 35%of its cost price,find the profit per cent.
2,Mr Mok deposits a sum of money in a bank at 5又2分之1 % p.a.Find the sum of money that Mr Mok deposits if he can get %2310 as simple interest after 3 years.
(Solution) Let x be the sum of money
3,Flora borrows $36000 from a finance company at 3,75% p.a. simple interest.If she has to return a total amount of $45450,how long does she borrow?
＊4,A cat and a dog are not satisfied with their weights.If the weight of the cat is increased by 20% while that of the dog is decreased by 10%,their weights will be the same.What percentage of the dog's original weight is the cat's original weight?

回答 (1)

胡雪8°

2012-08-14 10:43 am

✔ 最佳答案

1,
Discount
= $280 * 20%
= $56

Cost
= $56 ÷ 35%
= $160

Profit per cent
= [(280 - 56 - 160)/160) * 100%
= 40%

Alternative method :
Let R% be the profit per cent.

[280 * (20%/35%)] * R% = [280 * (1 - 20%)] - [280 * (20%/35%)]
1.6R = 64
R = 40

Hence, profit per cent = 40%

*****
2,
Let $x be the sum of money.

x * 5.5% * 3 = 2310
0.165x = 2310
x = 14000

The sum of money = $14000

*****
3,
Let n be the number of years she borrows.

36000 * (1 + 3.75%n) = 45450
1 + 0.0375n = 1.2625
0.0375n = 0.2625
n = 7

She borrows 7 years.

*****
4,
Let c be the original weight of the cat, while d be that of the dog.

c(1 + 20%) = d(1 - 10%)
1.2c = 0.9d
c = (0.9/1.2)d
c = 75%d

The cat's originalweight is 75% of the dog's original weight.

參考: 胡雪

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