F.3 Mathz Q3 More about %

2009-12-03 11:58 pm

1) A cuboid with a square base is 10cm high. If each side of its base reduces by 15 % , find the percentage change in its volume.

2)Class 3B is organizing a picnic where all participants must pay for it. Half of the money is for food and the other half is for bus rental is for bus rental.Some students suggest to hire an air-conditioned bus, but the rental is 20% more , If air0conditoned bus were finally hired, what would be the percenrage of the extra money each participant has to pay ?

3)If the percentage change in the mean age between 1981 and 1991 is +6-4% , the mean ahe of the local population in 1991 is 44-5 , find the mean age of the local population is 1981.
(correct yr answer to 1 d.p )

Please in detail =) Thank you !

回答 (1)

用戶9112

2009-12-05 7:54 pm

✔ 最佳答案

(1) The original volume = 10 * 10 * 10 = 1000 cm^3
The new side = 10 * (1 - 15%) = 8.5cm
The new volume = 8.5 * 8.5 * 8.5 = 614.125cm^3
The percentage decrease in volume = (1000 - 614.125)/1000 * 100% = 38.6% (1 dp)
(2) Let the original bus rental be $x
The original total expense = x + x = $2x
The air-cond bus rental = $x * (1 + 20%) = $1.2x
The new total expense = x + 1.2x = $2.2x
Percentage of extra money = (2.2x - 2x) / 2x * 100% = 0.2/2 * 100% = 10%
(3) Let the mean age in 1981 be x
(44.5 - x)/x = 6.4%
44.5 - x = 0.064x
1.064x = 44.5
x = 41.8
The mean age in 1981 was 41.8

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