The ratio of football cards to baseball cards is 5:2 and the ratio of baseball cards to basketball cards is 5:1. To solve this problem, we need the baseball card side of each ratio to be equal so we need to rewrite the ratios in terms of a common number of baseball cards. (Think of this like finding the common denominator when adding fractions.) The ratio of football to baseball cards can also be written as 25:10 and the ratio of baseball cards to basketball cards as 10:2. So, the ratio of football cards to basketball cards is football:baseball, baseball:basketball or 25:10, 10:2 which reduces to 25:2.

35% of the water consumption is industrial use and 15% is personal use so (35% - 15%) = 20% more water is used for industrial purposes. 10,000 gallons are consumed daily so industry consumes \( \frac{20}{100} \) x 10,000 gallons = 2,000 gallons.

To find the average of these 4 numbers add them together then divide by 4:

\( \frac{15 + 13 + 15 + 13}{4} \) = \( \frac{56}{4} \) = 14

If 90% of the town's 31,000 voters cast ballots the number of votes cast is:

(\( \frac{90}{100} \)) x 31,000 = \( \frac{2,790,000}{100} \) = 27,900

The mayor got 86% of the votes cast which is:

(\( \frac{86}{100} \)) x 27,900 = \( \frac{2,399,400}{100} \) = 23,994 votes.

To divide fractions, invert the second fraction and then multiply:

\( \frac{1}{6} \) ÷ \( \frac{4}{5} \) = \( \frac{1}{6} \) x \( \frac{5}{4} \)

To multiply fractions, multiply the numerators together and then multiply the denominators together:

\( \frac{1}{6} \) x \( \frac{5}{4} \) = \( \frac{1 x 5}{6 x 4} \) = \( \frac{5}{24} \) = \(\frac{5}{24}\)