My name is John Lau and I am a student at Piedmont Middle. I am in 8th Compute the sum of all tendigit numbers. Can you determine the sum of all n digit numbers? Hi John,Let us see how to find the sum of all three digit numbers. Answers for n digit numbers is similar. S = 100 + 101 + 102 + ..... + 999= (100 100) + (101100) +(102100) +...... +(999100) + 900 x 100 The last term is there since: there are 900, there digit numbers and you have subtracted 100 from each of these numbers. So, S= 0 + 1 + 2 + ..... + 899 + 90000 How to find the number of five digit numbers? Five digit numbers start with 10000 and end at 99999. From 1 to 99999 there are 99999 numbers. From 1 to 9999 there are 9999 numbers. So from 10000 to 99999 there are 99999  9999 = 90000 numbers. Cheers,Sukanta
