2011 AMC 10A Problem 8

Question

Last summer

30 \%

of the birds living on Town Lake were geese,

25 \%

were swans,

10 \%

were herons, and

35 \%

were ducks. What percent of the birds that were not swans were geese?

20

30

40

50

60

Use the percent that are not swans as the denominator

The desired percent is

\frac{30}{100-25}

WLOG, let there be

100

birds. Then

75

birds are not swans. The desired percentage is then

\dfrac{30}{75} \cdot 100 = 40 \%.

Thus, C is the correct answer.

Problem 8 in other years