中一數學代數問題~20點快唔該

1.Five times a certain number is greater than three times of the number by 16.Find the number.

let the number be x

5x=3x+16
5x-3x=16
2x=16
x=8

the number is 8.


2.The number of $2 coins that Tom has is three times the number of $5 coins.If Tom has a total of $88,find the number of $2 coins that he has.

let x be number of $2 coins Tom has.
let y be number of $5 coins Tom has.

x=3y ......(1)
2x+5y=88 .......(2)
Sub (1) in 2x+5y=88
2(3y)+5y=88
11y=88
y=8
sub y=8 in (1)
x=3*8
x=24

Tom has 24 $2 coins.

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2010-10-31 20:23:41 補充：
第一題應該是"let x be the number."
英文不好抱歉@@"

1. let X be the certain number
5X - 16 = 3X
5X - 3X = 16
2X = 16
X = 16/2
X =8
therefore, the certain number is 8

2. let Y be the number of $5 coin
2*3Y + 5Y = 88
6Y + 5Y = 88
11Y = 88
Y = 88/11
Y = 8
therefore, 3Y = 3*8 = 24
no of $2 coin is 24

1.
let n be the certain number
then 5n>3*16
5n>48
n>9.8
at least n should be the Integer,so n>10
ans:
the number at least is 10
2.
let n be tom's coins for $2
2*n+(5*n)/3=88
2n+5n/3=88
11n/3=88
n=24
ans.
he has 24 $2 coins