First of all you need to line them up.
8/20 - 2/5
Next you need to find a common denominator.
20 is a common denominator between the 2.
Then you change both denominators to the common one.
8/20=8/20, 2/5 x 4/4= 8/20
{Since 5x4=20, you have to do that on both sides to get the common denominator.}
Then you subtract
8/20 - 8/20 = 0.
So the answer is 0
Converting to twentieths, we get 8 over 20 minus 15 over 20, resulting in minus 7 over 20.
18/20 - 5/20 = 13/20
13/20 minus 3/5 is 1/20
14/20 - 3/5 = 14/20 - 12/20 = 2/20 = 1/10
14/20 minus 3/5 is 1/10
18/20 + 8/20 - 5/20 = 21/20 or 1 and 1/20
2/5 + 3/4 - 1/2 equals 8/20 + 15/20 - 10/20 which adds up to 8/20 This equals 4/5
31/20 minus 5/9 is 179/180
2 minus 2/5 plus 1/2 minus 4 = -1.9
1/4 - 1/10 = 5/20 - 2/20 = 3/20
2 minus 5/2 equals -1/2
3/4 minus 1/5 is 11/20