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1)
Method 1 :
Let a and b be the ages of Daisy and his brother respectively.

b = a - 2 ...... [1]
(a + 2)(b + 2) = 3a ...... [2]

Put [1] into [2] :
(a + 2)(a - 2 + 2) = 3(a + 2)
a² + 2a = 3a + 6
a² - a - 6 = 0
(a - 3)(a + 2) = 0
a = 3 or a = -2 (rejected)

Daisy is 3 years now.

Method 2 :
Let a be the age of Daisy.
Then, the age of her brother = a - 2

(a + 2)[(a - 2) + 2] = 3(a - 2)
a² + 2a = 3a + 6
a² - a - 6 = 0
(a - 3)(a + 2) = 0
a = 3 or a = -2 (rejected)

Daisy is 3 years now.


2)
Method 1 :
Let n be the number of sweets in each bag, and b be the number of bags.

b = n + 8 ...... [1]
bn = 384 ...... [2]

Put [1] into [2] :
(n + 8)n = 384
n² + 8n - 384 = 0
(n - 16)(n + 24) = 0
n = 16 or n = -24 (rejected)

There are 16 sweets in each bags.

Method 2 :
Let n be the number of sweets in each bag.
Then, number of bags = n + 8

n(n + 8) = 384
n² + 8n - 384 = 0
(n - 16)(n + 24) = 0
n = 16 or n = -24 (rejected)

There are 16 sweets in each bags.

2012-09-04 00:38:40 補充：
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