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The factors of 28 are [1, 2, 4, 7, 14, 28] and the factors of 40 are [1, 2, 4, 5, 8, 10, 20, 40]. They share 3 factors [1, 2, 4] making 4 the greatest factor 28 and 40 have in common.

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:

\( \sqrt{\frac{36}{25}} \)
\( \frac{\sqrt{36}}{\sqrt{25}} \)
\( \frac{\sqrt{6^2}}{\sqrt{5^2}} \)
\( \frac{6}{5} \)
1\(\frac{1}{5}\)

The least common multiple (LCM) is the smallest positive integer that is a multiple of two or more integers.

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

\( \frac{3}{9} \) x \( \frac{4}{5} \) = \( \frac{3 x 4}{9 x 5} \) = \( \frac{12}{45} \) = \(\frac{4}{15}\)