The number of times the digit 3 will be written when listing the integers from 1 to 1000 is
300
To find the number of times 3 occurs in listing the integer from 1 to 999. (since 3 does not occur in 1000). Any number between 1 to 999 is a 3 digit number xyzz where the digit x,y,z are any digits from 0 to 9.
Now, we first count the numbers in which 3 occurs once only. Since 3 can occur at one place in 3C1 ways, there are 3C1.(9×9) = 3.92 such numbers.
Again, 3 can occur in exactly two places in 3C1(9) such numbers. Lastly 3 can occur in all the three digits in one such number only 333.
∴The number of times 3 occurs is equal to 1×(3×92)+2×(3×9)+3×1=300.