呢條數唔係好明點計...

Define the number as xy

Not x times y, but x, y are the tens and units digit

Example: if the number is 12, then x=1, y=2

Then the original number is 10x+y
The new number is 10y+x
(you can get this conclusion easily)

So (10x+y) - (10y+x)=54 (because If the digits are reversed, the value of the number is decreased by 54.)

Solving, we get x-y=6 ...(1)

From the question, x+y=8...(2)

Adding (1) and (2)

2x=14
x=7

So by x+y=8, y=1

So therefore the original number is 71

You can easily check that this is the answer

Hope this can help you



Note: reversing the digits mean:

If 12 is reversed, then it becomes 21
If 83 is reversed, it becomes 38
If 123 is reversed, it becomes 321

條問題係解:
有一個兩位數
兩個單位加埋係8
如果呢個數調轉呢兩個位
數值就會低左54
問原數係幾多

for example
the original number is 42
the two digit are 4 and 2 sum of them are 6
if i reversed it,
it will become 24
the value of the number is decreased by 18

另外我俾埋呢條問題ge solution 你
let the ten digit number be x the digit number be y
x+y=8----------------(1)
10x+y-(10y+x)=54
10x+y-10y-x=54
9x-9y=54
x-y=6-----------------(2)
(1)+(2)
2x=14
x=7
y=1

i.e the original number is 71

如果2 個數字掉轉個位,, 俾原本果個少54 ,, 問你原本果個係咩

let x and y be the 2 number of 2 digits

x=8-y.....(1)
(10x+y)-54=10y+x ....(2) << 唔可以xy,, 因為咁樣會話左係x*y not 2個位的數字

sub (1) in (2)

80-10y+y-54=10y+8-y
-9y+26=9y+8
18y=18
y=1

sub y=1 in (1)
x=7

兩個數未加埋係8 ,
兩個數字的位置(十位同個位)掉轉左 ,個數值會下降54
求原本的數字
let x be the ten-digit no.
let y be the digit no.
x+y=8.......(1)
(10x+y)-54 = 10y+x.......(2)
From (1) ,x+y=8 ,x=8-y....(3)
From(2) ,10x+y)-54 = 10y+x
..............10x+y-10y-x=54
..............9x-9y=54
..............9(x-y)=9 (6)
..............x-y =6
..............x=6+y......(4)
sub(4) into (3)
6+y = 8-y
2y =8=6
y=1
sub y=1 into (3)
x= 8-1 =7
so the original number is 71
之後你可以check番 ,71-17=54~
所以係正確既~