1) If A is 40% less than B, what is the percentage that B is greater than A?
2) In a class, students take either History or Geography, but not both. If the number of students taking Geography is 50% more than those taking History, what is the percentage of students taking History?
3) If A is 36% less than B, what is the percentage that B is greater than A? Correct your answer to 3 significant figures.
4) If the price of petrol increases by 25%, by what percentage must a driver reduce his consumption in order to maintain the same expenditure as before?
5) In a library, the ratio of the number of Chinese books to the number of English books is 2 : 3. If 100 English books are added, the number of English books will increase to 65% of the total. Find the original number of books in the library. (Assume that the library contains Chinese and English books only.)
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Urgent!!! Percentagge 問題
2011-01-05 3:54 am
回答 (2)
2011-01-05 4:42 am
✔ 最佳答案
1) A = (1 - 40%)B = 0.6B
% tha B is greater than A
= [(B - A)/A] x 100%
= [(B - 0.6B)/0.6B] x 100%
= (66 and 2/3)%
2)
Let h be the number of students taking History, and g be the number of students taking Geography.
g = (1 + 50%)h = 1.5h
Percentage of students taking Geography
= [g/(g + h)] x 100%
= [1.5h/(1.5h + h)] x 100%
= 60%
3)
A = (1 - 36%)B = 0.64B
Percentage that B is greater than A
= [(B - A)/A] x 100%
= [(B - 0.64B)/0.64B] x 100%
= 56.3% (3 sig. fig.)
4)
Let r% be the reduction in consumption.
(1 + 25%)(1 - r%) = 100%
1 - r% = 20%
r = 80
The driver must reduce 80% of his consumption.
5)
Let 2k be the number of Chinese books, and 3k be the number of English books.
[(3k + 100)/(2k +3k + 100)] x 100% = 65%
[(3k + 100)/(5k + 100)] x 100% = 65%
300k + 10000 = 325k + 6500
25k = 3500
k = 140
Original number of books
= 2 x 140 + 3 x 140
= 700
2011-01-04 23:05:21 補充：
Sorry, wrong typing for Question 4). It should be:
Let r% be the reduction in consumption.
(1 + 25%)(1 - r%) = 100%
1 - r% = 80%
r = 20
The driver must reduce 20% of his consumption.
參考: micatkie, micatkie
2011-01-05 6:22 am
the original price of petrol(x):
y be the time of driving:
x(1+25%)(1-y%)=x
1-y%=0.8
-y%=-0.2
y=20
___________
So,the driver must reduce the driving time by 20%
y be the time of driving:
x(1+25%)(1-y%)=x
1-y%=0.8
-y%=-0.2
y=20
___________
So,the driver must reduce the driving time by 20%
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