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Let us take the number 52 and write it as

52 = 50 + 2 = 10 × 5 + 2

Similarly, the number 37 can be written as

37 = 10 × 3 + 7

In general, any two digit number ab made of digits a and b can be written as

ab = 10 × a + b = 10a + b

What about ba?

ba = 10 × b + a = 10b + a

In general, a 3-digit number abc made up of digits a, b and c is written as

abc = 100 × a + 10 × b + 1 × c

= 100a + 10b + c

In the same way,

cab = 100c + 10a + b

bca = 100b + 10c + a and so on.