Please help me to do Maths, thx!

Let X be the number of stamp that Jack need to give to Mary.

53+x = 2 * (70-x)
53+x = 140 - 2x
　3x = 87
　x = 29

So, Jace need to give may 29 stamps.


2007-04-16 09:15:21 補充：
最後果句打錯字,應該係：So, Jack needs to give Mary 29 stamps.

Assume X is no. of stamps Jack should give to Mary
70 - X = (53+70)/3
X = 70 - 41
X = 29

Jack should give 29 stamps to Mary, then Mary will have 82 stamps and Jack will have 41 stamps.

Let x be the stamps of Jack that after Mary gave the stamps to Mary.

( 53 + 70 ) / 3 = x
123 / 3 = x
x = 41

Hence, the stamps of Jack is 41 and the stamps of Mary is 41* 2 = 82.

Hence, the stamps that Jack should give to Mary is 70 - 41 = 29.

Let y be the number of stamp that Jack give to Mary

53+y = 2(70-y)
53+y = 140-2y
3y = 87
y = 29

Ans: Jack needs to give 29 stamps tp Mary.

Logical thinking:
(53+70)/3x2-53=29

In formula:
x = no. of stamps Mary has (53)
y = no. of stamps Jack has (70)
z = no. of stamps Jack gives Mary to get the result

by substituting into the formula 2(x+z) = y-z, z=29.

29
Total stamps=53+70=123
Since no. of stamps of Mary's : no. of stamps of Jack's = 2 : 1
So, no. of stamps of Mary's = 2/(2+1)*123
= 82
So, no. of stamps of Mary's received from that of Jack's =82-53
= 29

find the total number of stamps first: 53+70=123
In order to make the number of Mary's stamps twice that of Jack's,the ratio should be 1:2(jack:mary) that's mean the total number should divied by3parts(1+2), and mary will get two parts of it, jack get 1 parts. This can make the number of Mary's stamps twice that of Jack's.

[(53+70)/3*2]-53=29