Problem 318
Which of the following numbers are prime, and how do you know?
a. 97 b. 51 c. 143 d. 223
Solution
a. Prime. Because It is not divisible by any prime less than 10.
b. Not prime. Because it is divisible by 3 and 17.
c. Not prime. Because it is divisible by 11 and 13.
d. Prime. Because it is not divisible by any prime less than 15.