7. Marta escribió en su libreta los nùmeros \( 17,13,5,10,14,9,12 \) y 16 y calculó su promedio; después tachó dos números de la lista y notó que el promedio cra cl mismo. ¿Cuáles son los números qué achó Marta? \( \begin{array}{lllll}\text { (a) } 12 \text { y } 17 & \text { (b) } 5 \text { y } 17 & \text { (c) } 9 \text { y } 16 & \text { (d) } 10 \text { y } 12 & \text { (c) } 14 \text { y } 10\end{array} \)

\( \frac{3}{\frac{3}{4}} \) of \( \frac{4}{9} \div 9 \frac{1}{2} \)

If \( 3^2 \) is calculated, what is the result?

What is the absolute value of \( -12 + 4 \)?

number of girls is \( 9: 7 \). Find the number of boys if the total number of students is 3200 . 19. The sides of a triangle are in the ratio of \( 2: 3: 4 \). If the perimeter is 72 cm , find its sides. 20. In a factory the ratio of number of defective bolts produced to the number of good bulbs is \( 1: 10 \). In one hour the factory produced 330 bolts. Find the number of defective bulbs produced by the

Find the absolute value of \( 5 \).