A cricket team has won 40% of the 30 matches it has played so far this season, and 20 matches are still to be played. To finish the season having won 60% of all its matches, the team must win at least how many of the remaining matches?

So far it has won $0.40\times 30=12$ matches, and the season has 30 + 20 = 50 matches in all. Winning 60% of 50 means 30 wins in total, so 30 − 12 = 18 of the remaining 20 must be won. (Taking 60% of the 20 matches still to come gives 12 and quietly changes what the 60% is measured on — it is the whole season, not the rest of it.)