Mariana and Clarisa can together do a work in 5 minutes. If Mariana alone can do the work in 30 minutes, how long will it take for Clarisa to do it alone?

A shopkeeper sells two qualities of rice at the rates of $44 per kg. and $54 per kg, gaining 10% and 20% profit respectively. If he mixes the two variants in the ratio 2:3 and sells the mixture at $55.9 per kg., what is his gain or loss?

A box contains 4 purple and 6 white balls. Jessica takes out a ball, puts it back, and then takes out another ball. What is the probability that both balls were purple?