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f.3 math.. percentages!

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1. The area of a square is 256 cm2 .If each side of the square is cut by 25%, what is the percentage change in its area?2. If the radius of a circle is increased by 10%, find the percentage increase in its area.3. There are 800 students in a school, 37.5% of them are girls. If the numbers ... 顯示更多 1. The area of a square is 256 cm2 .If each side of the square is cut by 25%, what is the percentage change in its area? 2. If the radius of a circle is increased by 10%, find the percentage increase in its area. 3. There are 800 students in a school, 37.5% of them are girls. If the numbers of boys and girls are increased by 20% and 10% respectively,what is the percentage in the number of students? thank you very much!!

最佳解答:

1. The area of a square is 256 cm2 .If each side of the square is cut by 25%, what is the percentage change in its area? Ans: the percetage change = (1-0.25)(1-0.25)/1=0.5625=56.25%// 2. If the radius of a circle is increased by 10%, find the percentage increase in its area. Ans: the percentage increase in its area=(1+10%)^2-1=1.21-1=0.21=21%// 3. There are 800 students in a school, 37.5% of them are girls. If the numbers of boys and girls are increased by 20% and 10% respectively,what is the percentage in the number of students? ANs: NEW NUMBER OF STUDENTS = 800*37.5%*1.1+800*62.5%*1.2=930 SO (800*37.5%*1.1)/930=35.5% are girls and 64.55 are boys. 2008-10-05 13:04:28 補充: 1. The area of a square is 256 cm2 .If each side of the square is cut by 25%, what is the percentage change in its area? Ans: the percetage change = 1-(1-0.25)(1-0.25)/1=0.5625=1-56.25%=-43.75 %//

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