Simple Equaions & 體積應用題

唔一定全部識曬先答。答少少都得。多少不是問題。

1)
In a school, 50% of the girls wear glasses while 280 of boys wear glasses. If the number of girls wearing glasses is 2/7 of the number of boys, find the number of girls.
2)
You know how to do the following multiplication:12(10+3)=12(10)+12(3)=120+36=156.
We can do the same way for algebraic expressions.
e.g. x(x+1)
=x(x)+x(1)
=x二次方 +x
Try to do the multiplications of the following algebraic expressions.
a) 2x(3x-4)
b)(9-m)(4m)
3)
We can do arithmetic operations for directed numbers of fractions.
e.g.
圖片參考：http://us.f6.yahoofs.com/hkblog/nxmf8DaGGRkSUBH9Xooahcnu60OH8mONxw--_1/blog/20080821013441137.jpg.jpg?ib_____DdZ3fpRVe


Try to do the following questions.

圖片參考：http://us.f6.yahoofs.com/hkblog/nxmf8DaGGRkSUBH9Xooahcnu60OH8mONxw--_1/blog/20080821013455706.jpg.jpg?ib_____DYyS9TMf4



圖片參考：http://us.f6.yahoofs.com/hkblog/nxmf8DaGGRkSUBH9Xooahcnu60OH8mONxw--_1/blog/20080821013506750.jpg.jpg?ib_____D0_UVYwoq

4)
Find the volume of the following soild with a uniform cross - section which consists of a triangle and a trapezium.
Cross-sectional area
=
Volume
=
附圖：
圖片參考：http://us.f6.yahoofs.com/hkblog/nxmf8DaGGRkSUBH9Xooahcnu60OH8mONxw--_1/blog/20080821015104552.jpg.jpg?ib_____DWu.rqJbL

5)
Write down a percentage with a value greater than 23/25.
6)
A hawker spent $180 to buy 600 toy balls. The hawker is going to sell the balls. Suggest the selling price for each toy ball such that he can get a profit percentage of at least 40% after all the balls are sold.
7)
The original weights of Chris and Anna were 72 kg and 66 kg respectively. After joinning a slimming programme, both of them lost some weight. If Chris lost 20% of his weight, what is the possible percentage decrease in Anna's weight so that the difference between their weights is less than 4 kg?