A factorial has the form n! and is the product of the integer (n) and all the positive integers below it. For example, 5! = 5 x 4 x 3 x 2 x 1 = 120.

The factors of 80 are [1, 2, 4, 5, 8, 10, 16, 20, 40, 80] and the factors of 20 are [1, 2, 4, 5, 10, 20]. They share 6 factors [1, 2, 4, 5, 10, 20] making 20 the greatest factor 80 and 20 have in common.

There are 4 2-passenger taxis available so that's 4 x 2 = 8 total seats. There are 12 people needing transportation leaving 12 - 8 = 4 who will have to find other transportation.

To add these fractions, first find the lowest common multiple of their denominators. The first few multiples of 3 are [3, 6, 9, 12, 15, 18, 21, 24, 27, 30] and the first few multiples of 5 are [5, 10, 15, 20, 25, 30, 35, 40, 45, 50]. The first few multiples they share are [15, 30, 45, 60, 75] making 15 the smallest multiple 3 and 5 share.

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

\( \frac{2 x 5}{3 x 5} \) + \( \frac{9 x 3}{5 x 3} \)

\( \frac{10}{15} \) + \( \frac{27}{15} \)

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

\( \frac{10 + 27}{15} \) = \( \frac{37}{15} \) = 2\(\frac{7}{15}\)

An integer is any whole number, including zero. An integer can be either positive or negative. Examples include -77, -1, 0, 55, 119.