數學F.1

1. Let the smallest even number be 2m

then the other two are 2m + 2 and 2m + 4 respectively


2m + (2m + 2) + (2m + 4) = 42

6m + 6 = 42

6m = 36

m = 6

So, the smallest number is 2 X 6 = 12

And the other two are (12 + 2) and (12 + 4) = 14 and 16



2. Let the smallest even number be 2m + 1

then the other two are 2m + 3 and 2m + 5 respectively


(2m + 1) + (2m + 3) + (2m + 5) = 81

6m + 9 = 81

6m = 72

m = 12

So, the smallest number is 2 X 12 + 1 = 25

And the other two are (25 + 2) and (25 + 4) = 27 and 29

1) Let y ,(y+2),(y+4) be the 1st,2nd and 3rd no respectively.
y+(y+2)+(y+4)=42
3y+6=42
3y=36
y=12
Since,y=12,y+2=14 and y+4=16
Therefore,the 1st no is 12, 2nd no is 14 and the 3rd no is 16


2) Let a,(a+2),(a+4) be the 1st,2nd,and the 3rd no respectively
a+(a+2)+(a+4)=81
3a+6=81
3a=75
a=25
Since,a=25,a+2=27 and a+4=29
Therfore,the 1st no is 25,the 2nd no is 27 and the 3rd no is 29

Hope these answers can help you~
If you have any questions in the future,you can ask me~

let x be the smallest number
x+(x+2)+(x+4)=42
3x+6=42
3x=36
x=12
The three numbers are 12,14,16
let x be the smallest number
x+(x+2)+(x+4)=81
3x+6=81
3x=75
x=25
The three numbers are 25,27,29

a) let x係第一個even no, 另外兩個even number就係x+2同x+4
x+(x+2)+(x+4)=42
3x+6=42
3x=36
x=12

所以3個no,係12,14,16

b) let y係第一個even no, 另外兩個even number就係y+2同y+4
y+(y+2)+(y+4)=81
3y+6=81
3y=75
y=25

所以3個no.係25,27,29