Answer: 6 white dandelions.

Solution: A blooming dandelion is white on the fourth and fifth day. Therefore, on Saturday, the dandelions that bloomed on Tuesday or Wednesday will be white. Let's determine how many there are.

14 dandelions that were white on Monday had all their seeds dispersed by Wednesday, while 20 yellow ones definitely survived until Wednesday (possibly turning white).

On Wednesday, there were $15+11=26$ dandelions on the meadow. We know that 20 of them were on the meadow since Monday, and the remaining $26-20=6$ bloomed on Tuesday and Wednesday.

Comment: It is not hard to notice that the number of white dandelions on Monday does not affect the answer.
Problem 4. In the morning, a dandelion blooms, it flowers yellow for three days, on the fourth day in the morning it turns white, and by the evening of the fifth day, it withers. On Monday afternoon, there were 20 yellow and 14 white dandelions on the meadow, and on Wednesday there were 15 yellow and 11 white. How many white dandelions will there be on the meadow on Saturday?

[6 points] (D.E. Shnol)