maths 一题(Form 1 程度)

AB: PQ = 2 : 5
Let AB = 2h cm and PQ = 5h cm

BC : QR = 5 : 3
Let BC = 5k cm and QR = 3k cm

Area of ABCD = 70 cm²
AB x BC = 70 cm²
2h x 5k = 70
10 hk = 70
hk = 7

Area of PQRS
= PQ x QR
= 5h x 3k cm²
= 15hk cm²
= 15 x 10 cm²
= 150 cm²

用最小公倍數
e.g.一個長方形面積係63
3 | 63
|___
31
so,3x31=63
so,3=闊
31=長