Answer :
The expression 20-30 can be solved as:
[tex]20-30=20-(20+10)=20-20-10=0-10=-10[/tex]In a ruler, we can draw this expression as:

The expression 20-30 can be solved as:
[tex]20-30=20-(20+10)=20-20-10=0-10=-10[/tex]In a ruler, we can draw this expression as: