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

\( \frac{15 + 7 + 13 + 9}{4} \) = \( \frac{44}{4} \) = 11

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.

You have 2 out of the total of 50 raffle tickets sold so you have a (\( \frac{2}{50} \)) x 100 = \( \frac{2 \times 100}{50} \) = \( \frac{200}{50} \) = 4% chance to win the raffle.

To take the square root of a fraction, break the fraction into two separate roots then calculate the square root of the numerator and denominator separately:

\( \sqrt{\frac{81}{36}} \)
\( \frac{\sqrt{81}}{\sqrt{36}} \)
\( \frac{\sqrt{9^2}}{\sqrt{6^2}} \)
\( \frac{9}{6} \)
1\(\frac{1}{2}\)

To divide terms with radicals, divide the coefficients and radicands separately:

\( \frac{6\sqrt{4}}{3\sqrt{2}} \)
\( \frac{6}{3} \) \( \sqrt{\frac{4}{2}} \)
2 \( \sqrt{2} \)