How many 6 digit telephone numbers can be constructed with the digits 0, 1, 2, ..., 9 if each number starts with 35 and no digit appears more than once?

• the first two digits are fixed. so the rest of the 4 digits can be chosen from 8 remaining digits.
  
  so ans is 8P4= 1680
  
• 12 years agoHelpfull: Yes(16) No(2)
• 35---- is the phone number format.8 ways of filling 1st blank space.7 ways of filling next blank space. then 6,then 5. therefore we can have 8*7*6*5=1680 ways of filling. hence answer is 1680
• 12 years agoHelpfull: Yes(11) No(2)
• first 2numbers are 3 and 5.
  we should select 4 others numbers from remaining 8 numbers.............
  so TOTAL TELEPHONE NUMBERS=8P4=1680
• 12 years agoHelpfull: Yes(2) No(0)
• According to me answer will be- 1680
  
  Lets mark 6 places for 6 digits..
  - - - - - -
  At first 2 places numbers are fixed 3 & 5 so no. of ways of selecting them is only 1.
  Now at 3rd place the no. of ways of selecting 1 digit from availalbe 8 digits is 8C1
  As it is given tht Repeatation is not allowed.
  So
  For 4th place the no. of ways of selecting 1 digit from availalbe 7 digits is 7C1
  similarly for 5th and 6th place...
  1 1 8c1 7c1 6c1 5c1
  
  So finally, No of digits will be= 1 * 1 * 8c1 * 7c1 * 6c1 * 5c1
  = 1*1*8*7*6*5
  = 1680
• 12 years agoHelpfull: Yes(2) No(0)
• i think 25 can be arranged in 2 ways ie.2! and remaing 4 position can be seen by 8p4 ways =2!*1680=3360
• 12 years agoHelpfull: Yes(1) No(5)
• rest is 8 digits
  so 8p4=1680
  
• 12 years agoHelpfull: Yes(1) No(0)
• we have to make telephone no. having 6 digits _ _ _ _ _ _ these are 6 places
  1 1 8 7 6 5
  now we have only one option to fill 1st and 2nd position by 3 and 5 resp.so way of filling these positions is one.now out of 10 digits(0 to9)we are left with 8 digits as repetion is not allowed.so we have 8 choices to fill 3rd position and 7 choices for 4th position and so on.....and so 5 choices to fill 6th position.(now see above in first line). now multiply 1*1*8*7*6*5=1680
• 12 years agoHelpfull: Yes(1) No(0)
• Since there are 6 digits
  _ _ _ _ _ _
  
  number starts with 35 so
  3 5 _ _ _ _
  The trick is to start from the last digit:
  Now since there is a 0 in the list we cant place a zero at the final position
  so the last digit is found by 8c1 i.e. 8
  3 5 _ _ _ 8
  Since if we eliminate any number in the last position there are still 8 numbers so the second last position is again 8c1 i.e. 8 and then so on so forth is 7c1 and 6c1.
  Therefore the result is 8*8*7*6=2688
  
• 12 years agoHelpfull: Yes(0) No(3)
• fix two places as 3 5 , now four places are left and from 8 digits they can be filled without repeating,hence can be calculated as : 1*1*5*6*7*8=1680.
• 8 years agoHelpfull: Yes(0) No(0)