Question

If the natural numbers starting from 1 are written one after the other to form a 121-digit number, then what will be the last digit of the resultant number

Answer 1

The answer will be simply 121 because all numbers leaving 0are natural numbers

Answer 2

Answer:

1.

Step-by-step explanation:

Given,

There might be an easier way to do this, but this one is the one I came up with at first.

So first 9 numbers add up to 9 digits. The numbers 10 to 99 sum up to 90 numbers, each 2 digits long. Therefor 180 digits. So writing down 1 to 99 will result in 189 digits.

100 to 999 takes 2700 digits, so writing down 1 to 999, one needs 2889 digits.

1000 to 9999 takes 36000 digits, so 38889 digits in total.

10000 to 99999 takes 450000 digits, so in total we have 488889 digits. Close to the 500000.

Now we have 11111 digits left. And the next numbers will be 6 digits long. So 11111/6 is 1851 rounded down. So if we would write the next 1851 numbers down we would end with 499995 digits. And the last number we wrote down would be 101850. Then comes the number that fills and exceeds 500.000 digits: 101851.

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