f.3 maths問題 (20點!!!!!!!!)

1.Given that x>5, represent the values of y by inequalities in following questions.
a)y=1/5 x b)y=7x-4
2.A company purchased 100 T-shirts. The original price of each T-shirt is $10. Later on, the company found that 10 of them are damaged. In order to make 50% profit at least, the company decided to sell the rest at a price of $y each. Find the minimum value of y and lowest price of each T-shirt.(Correct the answer to the nearest dollar)
3.If the principal is $20000 and the interest rate is 5% p.a., find the simple interest and the amount after two years.
4.If the principal is $30,000 and the interest rate is 6% p.a. compounded half-yearly, find the compound interest and the amount after three years. (Correct the answers to the nearest dollars.)
5.The value of a computer is $12000. If its depreciation rate is 10% each year, find its value after four years.
6.In a secondary school, 80 students joined the girl guides last year. This year the number of participants has increased by 12.5%. It is expected that there will be 10% less in next year. Find the expected numbers of participants.
7.The rateable value of a flat is $800,000. Find the rates payable quarterly.
8.The property tax payable by Mr. Chan this year is $7920. If the property tax rate is 15%, find the monthly rent.
9.The length of each side of a square is 20 cm. If it is increased by 10%, find the percentage change in its perimeter.
10.If the length of a rectangle is reduced by 20% and its width is increased by 15%, find the percentage change in its area.
11.The total monthly income of Derek's family is $45000.If he is entitled to $350000 allowance, find his salary tax.
12.The salary tax of Mosses this year is $7200.If he is entitled to $130000 allowance, find his total annual income.
13.Roy is going to make an investment. If he wants to have a minimum return of double his principal in five years, what should be the corresponding interest rate? Find out one possible interest rate and verify it.