A game was conducted in a typewriting class, where a candidate has to type/enter all the three-digit numbers without space. If made a mistake while typing, the candidate can use the backspace key once for one three-digit number. What is the least number of times a candidate has to press the keys to type all the three-digit numbers? (Assuming the candidate did not make any mistake)

A typist starts to type the serial numbers of candidates in a list, upto 500. Minimum how many times does he need to press the keys of numerals only?

A typist started typing the serial numbers of 600 students in a list, then how many times he has to press the numeric keys?180016891692600

How many times do you have to write the digit '3', while writing numbers from 1 to 1000?

5. There are three keys for three suitcases with different locks. Each key only fits one of them. What is the minimum number of trials needed to find a key for each?23456789

A person must enter a 4 digit code to gain access to his cell phone. He will enter codes until he is successful, however he cannot try more than 3 times or the phone will lock him out. Let S denote a successful attempt and F denote a failed attempt. What is the sample space for this random experime