21. Choose all that are true. \( \begin{array}{l}\square \frac{1}{12} \times \frac{3}{4}=\frac{49}{16} \\ 8 \frac{5}{6} \times 2=17 \frac{2}{3} \\ 5 \frac{1}{2} \times 5 \frac{1}{2}=30 \frac{1}{4} \\ 9 \frac{1}{5} \times \frac{3}{5}=9 \frac{4}{5} \\ 6 \frac{3}{4} \times 3 \frac{1}{4}=19\end{array} \)

Alright, let’s break down these options and have some fun with them! First up, when you multiply fractions like \(\frac{1}{12} \times \frac{3}{4}\), you actually get \(\frac{1 \times 3}{12 \times 4} = \frac{3}{48}\), which simplifies to \(\frac{1}{16}\), not \(\frac{49}{16}\)! So that one's false. Now for \(8 \frac{5}{6} \times 2\), converting the mixed number gives us \(\frac{53}{6}\), and multiplying it by 2 yields \(\frac{106}{6} = 17 \frac{2}{3}\), so that's a winner! Next, \(5 \frac{1}{2} \times 5 \frac{1}{2}\) transforms into \(\frac{11}{2} \times \frac{11}{2} = \frac{121}{4}\), which is equal to \(30 \frac{1}{4}\). Well done! Then, looking at \(9 \frac{1}{5} \times \frac{3}{5}\) gives us \(\frac{46}{5} \times \frac{3}{5} = \frac{138}{25} = 5 \frac{13}{25}\), but we need a closer inspection for \(\frac{4}{5}\), so that's false! Finally, \(6 \frac{3}{4} \times 3 \frac{1}{4}\) computes to \(\frac{27}{4} \times \frac{13}{4} = \frac{351}{16}\), which is about \(21.9375\), meaning 19 isn’t correct either! So the true statements are: - \(8 \frac{5}{6} \times 2 = 17 \frac{2}{3}\) - \(5 \frac{1}{2} \times 5 \frac{1}{2} = 30 \frac{1}{4}\)