To subtract these fractions, first find the lowest common multiple of their denominators. The first few multiples of 9 are [9, 18, 27, 36, 45, 54, 63, 72, 81, 90] and the first few multiples of 15 are [15, 30, 45, 60, 75, 90]. The first few multiples they share are [45, 90] making 45 the smallest multiple 9 and 15 share.

Next, convert the fractions so each denominator equals the lowest common multiple:

\( \frac{9 x 5}{9 x 5} \) - \( \frac{9 x 3}{15 x 3} \)

\( \frac{45}{45} \) - \( \frac{27}{45} \)

Now, because the fractions share a common denominator, you can subtract them:

\( \frac{45 - 27}{45} \) = \( \frac{18}{45} \) = \(\frac{2}{5}\)

51% of the water consumption is industrial use and 35% is personal use so (51% - 35%) = 16% more water is used for industrial purposes. 45,000 gallons are consumed daily so industry consumes \( \frac{16}{100} \) x 45,000 gallons = 7,200 gallons.

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

\( \frac{18 + 12 + 16 + 14}{4} \) = \( \frac{60}{4} \) = 15

Christine scored 87% on the test meaning she earned 87% of the possible points on the test. There were 140 possible points on the test so she earned 140 x 0.87 = 122 points. Each question is worth 2 points so she got \( \frac{122}{2} \) = 61 questions right.

To add these fractions, first find the lowest common multiple of their denominators. The first few multiples of 6 are [6, 12, 18, 24, 30, 36, 42, 48, 54, 60] and the first few multiples of 10 are [10, 20, 30, 40, 50, 60, 70, 80, 90]. The first few multiples they share are [30, 60, 90] making 30 the smallest multiple 6 and 10 share.

Next, convert the fractions so each denominator equals the lowest common multiple:

\( \frac{9 x 5}{6 x 5} \) + \( \frac{3 x 3}{10 x 3} \)

\( \frac{45}{30} \) + \( \frac{9}{30} \)

Now, because the fractions share a common denominator, you can add them:

\( \frac{45 + 9}{30} \) = \( \frac{54}{30} \) = 1\(\frac{4}{5}\)