The way i do it is I multiply everything by 10 to get rid of the denominators, so (x + 3/10) * 10 and (2/5)*10. That gets you 10x + 3 = 4. subtract 3 from both sides to isolate x so 10x = 1. Divide both sides by 10 so 10x/10 = 1/10. That leaves you with x = 0.1 if you simplify 1/10. Plug it back in to check. 0.1 + 3/10 = 2/5. 2/5 = 0.4 if you simplify. 3/10 = 0.3 if you simplify. 0.1 +0.3 = 0.4. 0.1 + 0.3 Does add up to 0.4, so x = 0.1.
