First, you have to make them into decimals to make it easier. 2/8 equals 0.25.
1/5 and 2/10 equal 0.2. 0.2+0.2+0.25 equals 0.65 so if you suppose Jon's money is 1 dollar, he has 35 cents left. In a fraction, 0.35 is 35/100. If you simplify 35/100, it's 7/20.
Answer: Jon has 35/100 or 7/20 or his money left.
I hope it helps!