maths 急!!!!!!!!!~~

1.
Let bo be the original base of the triangle, and ho bethe original height.
When the new base becomes bo(1 + 60%), let h be the new height.

New area = Original area
bo(1 + 60%)h = boho
1.6h = ho
b = 0.625ho

Change in the height of the triangle
= [(0.625ho - ho)/ho] × 100%
= -37.5%
(decreased by 37.5%)


====
2.
Tax for the first $40000
= $40000 × 2%
= $800

Tax for the first $80000
= $800 + $40000 × 7%
= $3600 < $4500

Tax for the first $120000
= $3600 + $40000 × 12%
= $8400 > $4500

Let $(80000 + y) be her net chargeable income.

3600 + 12%y = 4500
3600 + 0.12y = 4500
0.12y = 900
y = 7500

Her net chargeable income
= $(80000 + 7500)
= $87500

2014-10-01 01:49:43 補充：
發問時點數已扣除，刪除答案只會損人不利己。

第二題你要先提供稅率。

http://www.ird.gov.hk/eng/pdf/pam61e.pdf

請看看是否跟從 2%, 7%, 12%, 17%
for (first $40,000, next $40,000, next $40,000, remainder)