Question

the proportion used to find the average number of trout you would expect to live in the pond is
$\frac{7}{20}=\frac{x}{400}$.
solve the proportion to find the expected number of trout in the population.
the expected number of trout in the population is

sample 1\tsample 2
catfish\t3\t5
bass\t9\t9
trout\t8\t6
all fish\t20\t20

Explanation:

Step1: Cross - multiply the proportion

$7\times400 = 20\times x$

Step2: Simplify the left - hand side

$2800=20x$

Step3: Solve for $x$

$x=\frac{2800}{20}=140$

Answer:

140