Question

The set $X=\{5,10,15,20,25\}$ can be written in Set-builder form as:

• A. $X=\{y:y=5a,a\in N,a<5\}$
• B. $X=\{y:y=5a,a\in N,a\le 5\}$
• C. $X=\{y:y=5a,a\in N,a\le 6\}$

Answer 1

The correct option is B $X=\{y:y=5a,a\in N,a\le 5\}$

Given $X=\{5,10,15,20,25\}$
Identifying the pattern, we see the elements to be first $5$ multiples of $5.$

In Set-builder form, if we assume $y$ to be the elements of the set, we can write the set as:
$X=\{y:y=5a,a\in N,a\le 5\}$