Latest TCS Aptitude Question SOLUTION: Suppose there is a number 235 such that sum of first two digits is equal to the third digit. How many such 3 digits numbers are possible?

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Suppose there is a number 235 such that sum of first two digits is equal to the third digit. How many such 3 digits numbers are possible?

Asked In TCS Sri Reddy (10 years ago)

Solved Saraswathy Read Solution (4)

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Read Solution (4) :

Saraswathy  (10 years ago)

The last digit can not be 0.

If the last digit is 1, the only possible number is 101.
(Note that 011 is not a 3-digit number)

If the last digit is 2, the possible numbers are 202 and
112.

If the last digit is 3, the possible numbers are 303, 213
and 123.

If the last digit is 4, the possible numbers are 404, 314,
224 and 134.

If the last digit is 5, the possible numbers are 505, 415,
325, 235 and 145.

Note the pattern here - If the last digit is 1, there is
only one number. If the last digit is 2, there are two
numbers. If the last digit is 3, there are three numbers.
If the last digit is 4, there are four numbers. If the last
digit is 5, there are five numbers. And so on.....

Thus, total numbers are
1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = 45

So Ans is 45 only

Is this solution Helpfull? Yes (59) | No (1)  

Saraswathy  (10 years ago)

As we know that total digits are
0 ,1, 2, 3,4,5,6,7,8,9
if three digit no is xyz
this means x+y=z must hold
so we have to select two no out of 10

ans is 10 c 2=45

Ans : 45

Is this solution Helpfull? Yes (12) | No (2)  

karthikeyank  (9 years ago)

Ans is 45

101 last digit is one
202,112 last digit is 2

if last digit is one it comes one time
if last digit is two it comes two time
so
1+2+3+4+5+6+7+8+9=45

Is this solution Helpfull? Yes (2) | No (2)  

Anjali  (6 years ago)

As the 3rd digit must be greater than first digit and for 1 there are such 9 digits nd for 2 there are 8 digits nd so on so we can directly calculate the sum of first 9 natural numbers =9(9+1)/2=45.

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