1. [SOLVED] Probability

A list of numbers consists of p positive and n negative numbers. If a number is picked at random from this list, the probability that the number is positive is (3/5). What is the value of (n/p)?

a) 3/8
b) 5/8
c) 2/3
d) 3/2
e) 8/3

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2. Originally Posted by fabxx
A list of numbers consists of p positive and n negative numbers. If a number is picked at random from this list, the probability that the number is positive is (3/5). What is the value of (n/p)?

a) 3/8
b) 5/8
c) 2/3
d) 3/2
e) 8/3

$\frac{p}{p+n} = \frac{3}{5} \Rightarrow \frac{\frac{p}{n}}{\frac{p}{n} + 1} = \frac{3}{5} \, ....$
$\frac{p}{p+n} = \frac{3}{5} \Rightarrow \frac{\frac{p}{n}}{\frac{p}{n} + 1} = \frac{3}{5} \, ....$
Why $\frac{p}{p+n} = \frac{3}{5}$? Thanks