數學方程式(F.1)急!!!

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1) Let the age of his son be y, the age of Mr. Lee be z.

y + z = 53..........(1)

4(y - 4) = z - 4..........(2)

(1): y = 53 - z..........(3)

Put (3) into (2):

4(53 - z - 4) = z - 4

4(49 - z) = z - 4

196 - 4z = z - 4

200 = 5z

z = 40..........(4)

Put (4) into (1):

y + 40 = 53

y = 13

So, Mr. Lee is now 40 years old and his son is 13 years old.


2) Let the original number of chocolate be y.

{[1 - (1 / 3)]y - 2} / 2 = 9

(2y / 3) - 2 = 18

2y / 3 = 20

y = 30

So, there are originally 30 pieces of chocolate.


3) Let the saving of Sam and Ken be y and z respectively.

y + z = 1000..........(1)

(1 / 2)y + (1 / 3)z = 400..........(2)

From (1): y = 1000 - z..........(3)

Put (3) into (2):

(1 / 2)(1000 - z) + (1 / 3)z = 400

[3(1000 - z) + 2z] / 6 = 400

3000 - 3z + 2z = 2400

-z = -600

z = 600..........(4)

Put (4) into (1):

y + 600 = 1000

y = 400

So, Sam has $400 and Ken has $600.

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.The sum of the ages of Mr Lee and his son is 53. 4 years ago,the age of Mr Lee is 4 times that of his son.Find the ages of each of them.

2.Sarah gives one-third of a box of chocolate to her mother.She eats 2 pieces of chocolate from the rest.Then she divides the remaining evenly to her two younger brothers and each of her brothers get 9 pieces of chocolate.How many pieces of chocolate are there in the box?

3.The savings ofSam and Ken are $1000 altogether.They spends half and one-third of their savings respectively to celebrate their father 's birthday.If they spend $400 altogether,what are their savings respectively?