Answer: The experimental probability that the first cactus he comes across has white flowers is 16/51.
Step-by-step explanation:
Since,

Let W represents the event of occurrence of white flower and P represents the occurrence of purple flower,
Then, According to the question,
n(P) = 35 and n(W) = 16
Also, the total number of trials, n(S) = 35 + 16 = 51
Thus, the probability of occurring white flower is,
