Basic College Mathematics (9th Edition)

$5\times11$
In order to find the prime factorization by 55, we can try to divide 55 by the first prime number, 2. 55 is not divisible by 2 or 3, so we can divide it by the next prime, 5. $55\div5=11$ The number 11 itself is a prime number. Therefore, the prime factorization of 55 is $5\times11$.