最佳回答取４０分：一條ratio問題

{x:y=16:9----------(1)
{(x-7):(y+7)=1:1------(2)
From (1) 9x=16y-----(3)
From (2),x=y+14----(4)
Sub. (4)into(3)
9x=16y
9(y+14)=16y
9y+126=16y
7y=126
y=18

Sub. y=18 into (1)
x:y=16:9
9x=16(18)
x=32

.'.the original number of sweets that Tom has is32 and the original number of sweets that David has is 18

Let x be the original number of sweets that Tom has and
y be the original number of sweets that David has.
Then from the question
x:y=16:9
or x/y=16/9
9x=16y
x=(16/9)y
Tom gives 7 sweets to David, both of them will have the same number of sweets
x-7=y+7
x=y+14
(16/9)y=y+14
(7/9)y=14
y=18
x=(16/9)y=32
the original number of sweets that David has is 18