ith opposite signs. 15. \( (-5) \times 8= \) 16. \( \frac{-12}{6}= \) 17. \( 8(-4)= \) 18. \( 1 \cdot(-8)= \) 19. \( (-7) \cdot(-4)= \) 20. \( (-2) \div(-2)= \) 21. \( \frac{18}{(-6)}= \)

How to convert 600 seconds in minutes?

Add. \( \begin{array}{lll}\text { (a) } 3 \frac{1}{8}+3 \frac{5}{8} & \text { (b) } 2 \frac{5}{11} & \text { (c) } 3 \frac{9}{10}+2 \frac{3}{5} \\ \text { (d) } 5 \frac{1}{2}+8 \frac{1}{8} & \text { (e) } 1 \frac{1}{7}+2 \frac{3}{11} & \text { (f) } 6 \frac{2}{9} \\ \text { (g) } 4 \frac{3}{7}+5 \frac{1}{5} & \text { (h) } 2 \frac{4}{6}+3 \frac{7}{8} & \end{array} \)

Add. \( \begin{array}{ll}\text { (a) } 3 \frac{1}{8}+3 \frac{5}{8} & \text { (b) } 2 \frac{5}{11} \\ \text { (d) } 5 \frac{1}{2}+8 \frac{1}{8} & \text { (e) } 1 \frac{1}{7}+2 \frac{3}{11} \\ \text { (g) } 4 \frac{3}{7}+5 \frac{1}{5} & \text { (h) } 2 \frac{4}{6}+3 \frac{7}{8}\end{array} \)

Round 15.159 to the nearest ten. 

How many times greater is \( 9 \times 10^{100} \) than \( 3 \times 10^{-10} \) ?