How to subtract 4/5 and 3/10 in simplest form

First you must find a common denominator. In this case 10 will work. You then multiply the top number by whatever you multiplied the bottom number by. This is shown below:
4/5- 3/10 = 8/10- 3/10 
You can now solve this to get 5/10. This answer can then be reduced to 1/2. 

1- find a common denominator of 5 and 10. Their least common denominator is 10 so convert 4/5 to a fraction with a denominator of 10 ( 8/10). Now subtract 3/10 from 8/10 to get 5/10.