maths questions 2(5題20點：)

[匿名]

2009-08-24 11:38 pm

1.Last year, the marked price and the selling price of a new digital camera were $7200 and $6120 respectively. But this year the marked price and the selling price are adjusted to $6400 and $5600 respectively. In comparing the discount per cent of these 2 years, which one is larger?

2.Mr Mok deposits a sum of money in a bank at 5.5p.a. Find the sum of money that Mr mok deposits if he can get $2310 as somple interest after 3years.

3.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 % of dog's original weight is cat's original weight ?

4.May makes a dozen small candles melt and recast it into a large cylindrical candle of height 20 cm. If at first each small candle is a cylinder of radius 1 cm and height 9cm, find the radius of the large candle formed.

5. A cylindrical pen holder of base radius 4cm, height 12.5 cm doesn't have a lid. Find the total external surface area of the pen holder.

回答 (1)

Prof. Physics

2009-08-25 12:01 am

✔ 最佳答案

1. Discount for last year = (6120 - 7200) / 7200 X 100% = -15%

Discount for this year = (5600 - 6400) / 6400 X 100% = -12.5%

So, the discount per cent last year is larger.

2. Let A be the sum of money deposited

A(3 X 5.5%) = 2310

A = $14 000

3. Let x and y be the original weights of the car and the dog respectively.

x(1 + 20%) = y(1 - 10%)

1.2x = 0.9y

y = 4x/3

So, the percentage of dog's original weight is cat's original weight

= y/x X 100%

= 4/3 X 100%

= 400/3 %

4. Total volume of the small candles

= 12 X pir2h

= 12pi(1)2(9)

= 108 pi cm3

Let R be the radius of the large candle

piR2H = 108 pi

piR2(20) = 108 pi

Radius, R = 2.32 cm or -2.32 (rejected) (cor. to 3 sig. fig.)

5. Total surface area

= Base area + Curved surface area

= pir2 + 2pirh

= pi(4)2 + 2pi(4)(12.5)

= 116pi cm2

參考: Physics king

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