Answer:
[tex]\huge\boxed{\bf\:1}[/tex]
Step-by-step explanation:
At first, let's factorise the given three numbers.
[tex]12\\= 4 * 3*1\\= \underline {2*2*3*1}[/tex]
[tex]15\\= \underline{5*3*1}[/tex]
[tex]20\\= 4*5*1\\=\underline {2*2*5*1}[/tex]
Here, from the given factors, we can see that the three numbers (12, 15 & 20) don't have any common factors except for 1.
•°• The least numbers divisible by 12, 15 & 20 is 1.
[tex]\rule{150pt}{2pt}[/tex]