consider a no 235, where last digit is the sum of first two digit no eg- 2+3=5 , how many such 3-digit no are there ???

• bwtween 100 and 200 there are 9 such numbers
  101,112,123,134,145,156,167,178,189
  in the same way btwn 200 and 300
  202,213,224,235,246,257,268,279 =8 numbers totally
  so series continues as 9+8+7+6+5+4+3+2+1=45 numbers
• 10 years agoHelpfull: Yes(26) No(0)
• 45
  
  total combinatioons using 0 are 9
  total combinations using 1 as first digit are 8 similalry using 9 is 1
  9+8+7+6+5+4+3+2+1=45
• 10 years agoHelpfull: Yes(19) No(1)
• 189/819
  279/729
  369/639
  459/549
  909
  for 9 it gives 9 cases
  for 8 it gives 8 cases & so on....
  that is why 9+8+7+...1=45
• 10 years agoHelpfull: Yes(4) No(0)
• ans : 45
  we have digits 0-9
  for 1 combinations are 001 only like that
  for 2, 002,112
  for 3, 003,123,213
  for 4, 004,224,234,324 so like that we have
  for 5, 5 combinations etc add all these combinations
  1+2+3+4+5+6+7+8+9=45
• 10 years agoHelpfull: Yes(2) No(0)
• using 1 at hundredth place,we can get 7 no
  using 2 at hundredth place,we can get 6 no
  similarly 5,4,4,3,2,1 no.
  total=(7+6+5+4+4+3+2+1)=32
  
• 10 years agoHelpfull: Yes(0) No(6)
• 45
  9+8+7+6+5+4+3+2+1=45
• 10 years agoHelpfull: Yes(0) No(0)
• Fady Bro:-
  9+8+7+6+5+4+3+2+1 ;)
• 10 years agoHelpfull: Yes(0) No(2)