SOLUTION: the sum of the composite numbers between 20 and 30 ,minus the sum of the prime numbers less than 20

Algebra ->  Divisibility and Prime Numbers -> SOLUTION: the sum of the composite numbers between 20 and 30 ,minus the sum of the prime numbers less than 20       Log On


   

Question 851227: the sum of the composite numbers between 20 and 30 ,minus the sum of the prime numbers less than 20
Answer by JulietG(1812) About Me  (Show Source):
You can put this solution on YOUR website!
Composite numbers are those positive integers that are NOT prime.
In this case: 21, 22, 24, 25, 26, 27, 28
The prime numbers between 20-30 are 23, 29
If you add the composites, you get 173.
Add the primes to get 52.
Subtract 52 from 173 to get 121.
.
That's for the correct definition of 'between'. If it *includes* 20 and 30 (both composites), then the equation is 223-52=171.
(Do check my addition and subtraction.)