I hope your product design class covered error propagation, because one 1% 20 ohm resistor would still be cheaper and more precise than 4 5% 5 ohm resistors.
But four 5%-tolerance 5-ohm resistors could be chosen to add up to almost exactly 20 ohms, but a 20-ohm resistor would never be 20 ohms due to the notch.
In the old days, it might have been cheaper than the more accurate resistors. These days, high precision resistors are relatively inexpensive.
