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Lastly - Well

What are the last two digits of 2^(2^2003)?

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Lesser Digits

How many positive integers less than or equal to 4000 can be written down without using the digits 7, 8 or 9?

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Six Times Five

How many six digit numbers are there which DO NOT contain a 5?

Mini-max

Age 11 to 14 Challenge Level:

Consider all two digit numbers ($10$, $11$, . . . ,$99$). In writing down all these numbers, which digits occur least often, and which occur most often ?

What about three digit numbers, four digit numbers and so on?