By buying two shirts, Roger will save $18 x \( \frac{50}{100} \) = \( \frac{$18 x 50}{100} \) = \( \frac{$900}{100} \) = $9.00 on the second shirt.

So, his total cost will be
$18.00 + ($18.00 - $9.00)
$18.00 + $9.00
$27.00

A factor is a positive integer that divides evenly into a given number. For example, the factors of 8 are 1, 2, 4, and 8.

A rational number (or fraction) is represented as a ratio between two integers, a and b, and has the form \({a \over b}\) where a is the numerator and b is the denominator. An improper fraction (\({5 \over 3} \)) has a numerator with a greater absolute value than the denominator and can be converted into a mixed number (\(1 {2 \over 3} \)) which has a whole number part and a fractional part.

To add these fractions, first find the lowest common multiple of their denominators. The first few multiples of 2 are [2, 4, 6, 8, 10, 12, 14, 16, 18, 20] and the first few multiples of 4 are [4, 8, 12, 16, 20, 24, 28, 32, 36, 40]. The first few multiples they share are [4, 8, 12, 16, 20] making 4 the smallest multiple 2 and 4 share.

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

\( \frac{2 x 2}{2 x 2} \) + \( \frac{8 x 1}{4 x 1} \)

\( \frac{4}{4} \) + \( \frac{8}{4} \)

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

\( \frac{4 + 8}{4} \) = \( \frac{12}{4} \) = 3

The first few multiples of 8 are [8, 16, 24, 32, 40, 48, 56, 64, 72, 80] and the first few multiples of 12 are [12, 24, 36, 48, 60, 72, 84, 96]. The first few multiples they share are [24, 48, 72, 96] making 24 the smallest multiple 8 and 12 have in common.