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

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)

Ritika wants to type the first 160 natural numbers. The number of times she has to press thenumbered keys i

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

There is a standard numeric keypad on a mobile phone. You can only press the current button or buttons that are directly up, left, right, or down from it (for ex if you press 5, then pressing 2, 4, 6 & 8 are allowed). Diagonal movements and pressing the bottom row corner buttons (* and #) are prohibited.Given a number n, find the number of possible unique sequences of length n that you can create by pressing buttons. You can start from any digit.