1.There were 500 students in a tutorial centre last year. It is given than the number of students increases by 35% this year.
(a) Find the number of students of this year
(b)The tutorial centre expects that the number of students next year will increase by 20% compared with this year's. Find the number of students next year.
2.A shoe shop has two branches, A and B. The sales of branch A and B last year were $423 000 and $517 000 respectively. The sales of branch A this year has increased by 5% but that of branch B has decreased by 1% from last year's.
(a)Find the total sales of the shoe shop this year
(b)By what percentage has this year's total sales increased from last year's?
3.The total rainfall of a city this year is 10% more than last year, while the total rainfall last year was 4% more than two years ago. It is know than the total rainfall of the city this year is 2 917.2 mm.
(a)Find the total rainfall of the city two years ago.
(b)Find the percentage change in the total rainfall of the city in these three years.
4.The population of a city has increased by 10% each year in the past 5 years. It is given that the current population of the city is 805 255.
(a)Find the population of the city 2 years ago
(b)Find the population of the city 5 years ago
5.The depreciation rate of a mobile phone is 6% every 2 months. If the current value of the mobile phone is $2 850
(a)find the value of the mobile phone after 8 months. (Give your answer correct to the nearest dollar)
(b)find the percentage change in the value of the mobile phone in 8 months (Give your answer correct to 2 decimal places)
(c)after how many months will the value of the mobile phone drop below $2 000?
6.It is know that x=80. If x decreases by 20 and then decreases by 15%, what is the overall percentage change in x?
中學數學 中二數學
2012-12-28 4:47 pm
回答 (1)
2012-12-28 7:50 pm
✔ 最佳答案
1(a) The number of students of this year= 500 * (1 + 35%)= 675(b) The number of students next year= 675 * (1 + 20%)= 8102(a) Total sales of the shoe this year= 423000 * (1 + 5%) + 517000 * (1 - 1%)= 955980(b) (955980 - (423000 + 517000))/(423000 + 517000) * 100%= 1.7%3(a) Let the total rainfall of the city is x mm in two years agox(1 + 4%)(1 + 10%) = 2917.2 x = 2550(b) The percentage change in the total rainfall of the city in these three years= (2917.2 - 2550)/2550 * 100%= 14.4%4 The population of the city 2 years ago= 805255/1.1^2= 665500The population of the city 5 years ago= 805255/1.1^5= 5000005(a) The value of the mobile phone after 8 months= 2850 * (1 - 6%)^4= 2225.13(b) The percentage change in the value of the mobile phone in 8 months = (2225.13 - 2850)/2850 * 100%= -21.93%(c) 2850 * (1 - 6%)^x < 20000.94^x < 0.701754386Xlog0.94 < log0.701754386x > 5.72395156So, after 12 months, the value of the mobile phone drop below $2 0006 The new value of x is 80 * (1 - 20%) (1 - 15%) = 54.4overall percentage change in x= (54.4 - 80)/80 * 100%= -32%
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