De los estudiantes de un colegio \( 1 / 3 \) solo practican futbol, \( 2 / 7 \) solo practican baloncesto y \( 1 / 5 \) solo practican voleibol, ¿Qué fracción de los estudiantes representa la cantidad de estudiantes que juegan solo uno de estos tres deportes?

c) \( 8+(-18): 3= \)

\( 37 ; 33 ; 29 ; x ; 21 ; \ldots \). Write down the value of \( x \). Determine the \( n^{\text {th }} \) term of the number pattern. Determine the \( 15^{\text {th }} \) term of the sequence. Which term is the first to have a negative value.

Find \( -\frac{8}{15}-3 \frac{4}{5} \). Write your answer as a mixed number in simplest form.

Find \( \frac{5}{6}-\left(-\frac{3}{4}\right) \). Write your answer as a mixed number in simplest form.

10. A girl swims 400 m in still water and then returns to the initial point (from where she started) in 20 minutes. Determine the speed of the girl. 11. A man is running at a speed of \( 3 \mathrm{~m} / \mathrm{s} \) and covers some distance in 15 sec . Find the time taken by his pet dog to cover the same distance at a speed of \( 10 \mathrm{~m} / \mathrm{s} \).