#### Answer

$5\times11$

#### Work Step by Step

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 $5\times11$.