Answer:
615000 cfu
Explanation:
Original culture contains 20 ml
0.1 ml is taken from original culture and transferred to tube A contains 9.9 ml of water making 10 ml all together.
1 ml from tube A plated on plate A yields 305 colonies
10 ml will yield 3050 colonies
0.1 ml yielded 31 colonies
1 ml of the sample will yield 310 colonies
10 ml will yield 3100 colonies assuming that the mixture was mixed thoroughly
mean number of colonies in 10 ml yielded by the both plating = ( 3050 + 3100) / 2 = 3075 colonies
0.1 ml of the original sample contains 3075 colonies
20 ml will contain = (20 × 3075 colonies) / 0.1 = 615000 cfu
