lurgshall co.-swap

as per the lecture I followed of yours and whatever question I attempt in swap..I always get a diff of .10 in this case end result I got 5.35 but the answer is 5.45 50% (1 – 0.5 – 0.2) = 0.15 in this step ..the .2 difference is the culprit but I have no idea why is it there.. as per your lecture step I get .25 in each and subtracting the same gets me my end result .. but every question the diff happens..can you please explain why? or will the answer gain marks cos of the slight difference?