Let the two numbers be x and y.
According to your question;
x + y = 7 10y + x = 10x + y + 9
By equation 1 ; x = 7-y
Substituting the value of x ;
10y + ( 7 -y) = 10(7-y) + y + 9
9y + 7 = 70 -10y + y + 9
9y + 7 = 70 - 9y + 9
=> 18y = 70 -7 + 9 => 18y = 72 => y = 4
Substituting for x ;
x = 7 - y => x = 7 -4 => x = 3
Thus, x = 3 and y = 4; => The number is 34.
The original number is 34 .
The sum of its digits is (3 + 4) = 7 . Reversing its digits makes it 43 . . . 9 more than 34.
How I did it: (There must be a much more elegant mathematical method)
There are only 6 possibilities for the original number. They are . . .
16 25 34 43 52 61 .
Instead of trying to dream up a sophisticated equation, I decided it was faster and easier to just go down the list and look for one that worked. The third one I tried worked.
The two-digit number is 34. The sum of its digits is 7, and reversing its digits results in the number increasing by 9. The digits are identified as 3 and 4, meeting both conditions of the problem.
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Dalam bahasa Cina, sepupu disebut 表亲 (biǎo qīn) yang artinya kerabat sepupu dari pihak ibu atau campuran keluarga. Jika dari pihak ayah, disebut 堂亲 (táng qīn). Biasanya, orang Cina membedakan sepupu berdasarkan umur dan jenis kelamin, tapi 表亲 adalah istilah umum yang paling sering dipakai.