Ambersnyder, Your answer would be A).
Answer:
Tube 2 has a total dilution of 1:50
Explanation:
We have a 2 ml serum sample added to a 18 mL phosphate buffered saline sample in tube 1. This means now in tube 1 there is 20 mL.
We have a 1:10 (= 2:20) dilution here.
10 ml of this 1:10 diluted tube 1 is taken and added to a 40 mL of PBS in tube 2.
Now we have 50 mL in tube 2.
This is a 10:50 (= 1:5) dilution.
The total dilution is 10x5 = 50
So the total ditultion has a rate 1:50
Tube 2 has a total dilution of 1:50
