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Zorluk: ZorTwo-Way Tables and Probability

A botanist conducted an experiment to study the germination rates of seeds in two different soil mixtures, Mixture A and Mixture B. The results of the experiment are partially shown in the table below, where xx is a positive constant.

Soil MixtureGerminatedDid Not Germinate
Mixture Axx1212
Mixture B3030x+6x + 6

Of the seeds in the experiment that did not germinate, the probability that the seed was planted in Mixture A is 13\frac{1}{3}. Given that a seed selected at random from the experiment germinated, what is the probability that it was planted in Mixture A?

Cevap: 0.375

Cevap

3/8 (or 0.375)
To find the probability that a germinated seed was planted in Mixture A, we must first solve for the variable xx. The number of seeds in Mixture A that did not germinate is 1212, and the total number of seeds that did not germinate is 12+(x+6)=x+1812 + (x + 6) = x + 18. We are given that the probability a non-germinated seed was planted in Mixture A is 13\frac{1}{3}. Setting up the equation: 12x+18=13\frac{12}{x + 18} = \frac{1}{3} yields x+18=36x + 18 = 36, so x=18x = 18. Substituting this value back into the table, the number of germinated seeds in Mixture A is 1818. The total number of germinated seeds is the sum of germinated seeds in Mixture A and Mixture B: 18+30=4818 + 30 = 48. Thus, the probability that a germinated seed was planted in Mixture A is 1848\frac{18}{48}, which simplifies to 38\frac{3}{8} (or 0.3750.375).

Adım Adım Çözüm

1
Set up the conditional probability equation for seeds that did not germinate to find xx.
x=18x = 18
From the table, the number of seeds in Mixture A that did not germinate is 1212, and the number of seeds in Mixture B that did not germinate is x+6x + 6. The total number of seeds that did not germinate is 12+(x+6)=x+1812 + (x + 6) = x + 18. The probability that a seed that did not germinate was from Mixture A is 12x+18=13\frac{12}{x + 18} = \frac{1}{3}. Solving this equation gives 36=x+1836 = x + 18, which simplifies to x=18x = 18.
2
Find the number of germinated seeds in Mixture A and the total number of germinated seeds.
Mixture A germinated = 1818, Total germinated = 4848
Substituting x=18x = 18, the number of germinated seeds in Mixture A is 1818. The number of germinated seeds in Mixture B is given as 3030. The total number of germinated seeds is 18+30=4818 + 30 = 48.
3
Calculate the conditional probability that a germinated seed was planted in Mixture A.
38\frac{3}{8} or 0.3750.375
The probability is the number of germinated seeds in Mixture A divided by the total number of germinated seeds, which is 1848=38\frac{18}{48} = \frac{3}{8}, or 0.3750.375 as a decimal.

Anahtar Kavram

Conditional Probability in Two-Way Tables
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