Expert: Lynn Houston - 8/5/2008

Question
1.Which one of the following numbers is all prime numbers?
A. 2,3,5,9
B. 3,11,23,31
C. 2,5,15,19
D. 7,17,29,49

2. Which one of the following is a composite number?
A. 13
B. 63
C. 61
D. 31

3. A school custodian waxed a gymnasium floor that measured 20 feet by 20 feet. How many square feet did she have to wax?

 A. 400 square feet  
 B. 40 square feet
 C. 800 square feet
 D. 80 square feet  

Answer
A prime number is a number where the only factors are 1 and the number itself.  That is, it can't not be divided by any other number.  9 is divisable by 3, so it's not A.  15 is divisable by 5, so it's not C.  49 is divisable by 7, so it's not D.

2. A composite number is one that is NOT prime.  Nothing divides 13, but 1 and 13, 61 and 31 are both prime, so can't be a composite number.

3.  Area is length times width.  The length of the floor is 20 feet and so is the width, therefore 20 times 20 = 400 or 400 square feet.

Re-ask if something isn't clear.