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

• 55 ways
  10 ways when first digit is 0
  9 ways when first digit is 1
  .
  .
  .
  1 way when first digit is 9.
  Total = 10+9+...+1 = 55
• 14 years agoHelpfull: Yes(26) No(8)
• ur number is xy9
  now if x is 0 then y has 10 options
  now if x is 1 then y has 9 options (except 9)
  now if x is 2 then y has 8 options (except 9 and 8)
  .
  .
  .
  now if x is 9 then y has 1 option (that is 0)
  
  so the answer is 1 + 2 + ... + 10 = 55
• 12 years agoHelpfull: Yes(10) No(2)
• 55 is answer
• 8 years agoHelpfull: Yes(0) No(1)