You are helping to prepare food for a large family gathering. You can slice two zucchinis per minute. You need 30 sliced zucchinis. How long will it take you to finish, if you have already sliced 12 zucchinis?

So you still have to slice 18 of them

2 zuks take 1 min
so 1 will take 1/2 minute
then 18 will take 18(1/2) or 9 more minutes.