英數！！help~help！！plz

2011-12-24 5:55 am

7) An alloy contains 300g of copper and 450g of zine.If the weight of copper is increased by 30% and the weight of zine is decreased by 10%.

(a)What is the new weight of copper in the alloy?
(b)What is the new weight of zine in the alloy?
(c)Find the percentage change in the weight of the alloy.

8)The production cost of a book includes the following:
Typesetting:$20,000
Paper:$30,000
Printing:12,000
If the cost of typesetting,paper and printing are increased by 20%,5% and 10% respectively,find the percentage increase in the total production cost of the book.

9)The length and width of a rectangle are 15cm and 10cm respectively.If the length is decreased by 20% and the width is decreased by 10%.

(a)Find the new length of the rectangle.
(b)Find the new width of the rectangle.
(c)Find the new area of the rectangle.
(d)Find the percentage decrease in the area of the rectangle.

10) A car travels on a highway at a constant speed V km/h for t hours.If the speed of the car is increased by 10% and the time spent on travelling is decreased by 15%.Find the percentage change in the distance to be travelled.

回答 (1)

徐偉國

2011-12-24 6:32 am

✔ 最佳答案

7(a)new weight of copper
=300*(1+30%)
=390g
(b)new weight of zinc
=450*(1-10%)
=405g
(c)orginal weight of alloy
=300+450
=750g
new weight of the alloy
=390+405
=795g
percentage change=(795-750)/750*100%
=6%
8.original total production cost of the book
=20000+30000+12000
=$62000
new total production cost
=20000*(1+20%)+30000*(1+5%)+12000*(1+10%)
=24000+31500+13200
=$68700
percentage change=(68700-62000)/62000*100%
=10.8%(corr.to 3 sig.fig.)
9(a)new length of the rectangle
=15*(1-20%)
=15*80%
=12cm
new width of the rectangle
=10*(1-10%)
=9cm
new area of the rectangle
=12*9
=108cm^2
original area
=15*10
=150cm^2
percentage decrease
=(108-150)/150*100%
=-28%
10)original distance=Vt
new distance=V*(1+10%)*t*(1-15%)
=1.1V*0.85t
=0.935Vt
percentage change
=(0.935Vt-Vt)/Vt*100%
=-6.5%

參考: me

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