Question

How many 4-digit numbers are neither multiples of 2 nor multiples of 5?

Answer 1

smallest 4 digit number: 1000
largest 4 digit number : 9999
number of 4 digit number = 9999-1000+1 = 9000
of those 4500 will be divisible by 2
How many are divisible by 5? ...> 9000/5 or 1800
how many are divisible by both 2 and 5 ? , they have to end in 0
there are 9000/10 = 900 , we can't count those twice
number divisible by 2 or 5 = 4500 + 1800 - 900 = 5400

so, those not divisible by either 2 or 5 = 9000 - 5400 = 3600

Answer 2

thanks