Of the first 1000 natural numbers, how many of them have at least one zero, when expressed in base 7? Thank you for help.
You have 6 numbers between 10 and 60 =6
You have 13 numbers between 100 and 200 =13
13 x 6 = 78 numbers
You have 1 number for 1000.
So: 6 + 78 + 1 = 85 such numbers.
