To convert from a base 10 to a binary, start dividing by 2.

To convert 20 to base 2:

20 divided by 2 is 10 with0remainder.

10 divided by 2 is 5 with0remainder

5 divided by 2 is 2 with1remainder

2 divided by 2 is1with0remainder

Now, read off the result at the bottom and the remainders from bottom up.

10100

Now, you try 19 and so on