+3 votes
in Mathematics by kratos

For any natural number n, let (n) denote the sum of the digits of n. Find the number of all 3-digit numbers n such that ( *(n)) = 2.

1 Answer

+3 votes
by kratos
 
Best answer

Let n = abc

where n = a × 100 + b × 10 + c a three digit number

a + b + c = (n); Here note that (n) ≤ 27

Since ( (n)) = 2,

It means sum of digits of *(n) is 2

Now, (n) can be, (n) = 2, 11, 20 only

Now Case-1

a + b + c = 2; possible cases are {0, 1, 1} gives 2 number and {2,0, 0} gives 1 number (ex : 200)

Total number in case (1) are 3

Total in case (3) = (3 × 4 + 6 × 4) = 36 ways

Total numbers = 3 + 61 + 36 = 100

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