We know that 5 fifths make up a whole. The chef only needs 3/5 of that whole, so we still have 2 fifths remaining. Now, we have to subtract 50 by the number of lunch orders, 20. 50 subtracted by 20 is equal to 30, but we have to subtract a whole because of the fraction. We get the number 29. Then, we add the remaining fraction back. We get the answer as 29 2/5.