How Many Prime Numbers Are There?

1. How many prime numbers are less than 10?

2. How many prime numbers are between 10 and 20?

3. How many prime numbers are between 20 and 30?

4. How many prime numbers are between 30 and 40?

5. In a group of ten consecutive numbers > 10, what is the maximum number of primes there could be? (Hint: how many of the ten numbers MUST be even? Knock those out. What other multiples can you eliminate?) It might help to write the numbers down as a list and cross out the possibilities.