I know 5/12 is less than 1/2 because; when you turn the two numbers into decimals, you have these;
5/12= 0.416 approximately 0.4
1/2= 0.5
As you can see, 0.4 is a lot less than 0.5. So 5/12 is less. Also, 1/2 means half. So the half of a particular thing is usually bigger than the quarter or others. Hope i helped. Have a nice day.
