In how many ways can a lock be opened if that lock has three digit number lock if i) the last digit is 9ii) and sum of the first two digits is less than or equal to the last digit.numbers are from 0-9

Interview Candidate
Sep 13th, 2004
5
1604

Showing Answers 1 - 5 of 5 Answers

Gaurav

Dec 8th, 2005

61

Sucheta

Mar 30th, 2006

My ans is 55.. plz give the complete solution of this combination problem.

kiruba

Jun 20th, 2006

The condition is this that the sum of the first two digits shud be lesser than or equal to the last digit and given that the last digit is 9.so if the first digit is 0 then 0,1,2,3,4,5,6,7,8,9 can all be the second digit. thus for 0 the lock has 10 ways to be opened.likewise for 1 we have 0,1,2,3,4,5,6,7,8 thus there are 9 ways when the first digit is 1.so proceeding this way0 - 10 ways1- 9 ways2 - 8 ways3- 7 ways4-6 ways5-5 ways6-4 ways7 -3 ways8 - 2ways9 -1waysumming it all - 10+9+8+7+6+5+4+3+2+1 = 55.