Percentage for S3 Math

1. The costs of labour and cloth for making a dress are $500 and $125 respectively. If the cost of labour is increased by 10% and the cost of cloth is decreased by 20%, what is the percentage change in the cost of making the dress?
sol
cost of labour =500 *(1+10%)=$550
cost of cloth=125* (1+20%)=$150
percentage change=[(550+150)-(500+125)]/(500+125)*100%
=12%

2. A certain kind of bacteria grows by 50% in every hour. If the are 1000 bacteria at noon, find its population at 3 pm on the same day.
noon=12am
the time from 12am~3pm=15hrs
its population at 3 pm on the same day
=1000*(1+50%)^15 =437 893.89
3. Mr. Lee owns a flat with a rateable value of $144000. If the percentage of rateable value is 5% per year, what is the quarterly rates that he has to pay?
(144 000 * (5%)) / 4 = 1 800

4.The quartery rates payable of Mrs. Cheung for her flat in Shatin is $1100, if the annual percentage of rateable value is 5.5%, what is the rateable value of her flat?
(1 100 * 4) / (5.5%) = 80 000
5.Mr. Leung had to pay $1200 for the rates last year. After moving to another house, he now has to pay $1500 for the rates of the new flat. What is the percentage change in the rateable value of his new house?
(1500-1200)/ 1200*100%=25%

I help you to solve Q1 and Q2.
_________
$500(1+10%)+(1-20%)125-500-125/(500+125)
+4%
___________
1000(1+50%)^3
=3375
_______________

2010-11-01 23:30:48 補充：
noon唔係解中午咩?