In the football league of 2010, ManU won 40% of their games

The original source was probably an assistant coach at Liverpool.

Anyway:

I. Assign Values:
Pick simple numbers

Let the # of 1st year games = 10
Let the # of 2nd year games = 30 (= "thrice" 10)

# of games won, 1st year:
40% = (.4 * 10) = 4

# of games won, 2nd yr:
60% = (.6 * 30) = 18
Total games won: (18+4) = 22
Total games played: (10+30) = 40

Overall percent won?
\((\frac{GamesWon}{Total Games}*100)=(\frac{22}{40}*100)=\)

\(.55*100=55\) %

Answer D

II. Weighted average

"Weight" the win percents from the ratio of number of games, which is 1 : 3
40% = .40 weighs 1
60% = .60 weighs 3
Total weight= (1 + 3) = 4

(You can use variables for weights but they're not necessary. x and 3x would get canceled out in the division by the total of the ratio parts, 4x)

\(\frac{.40(1) + .60(3)}{4}=\frac{.4+1.8}{4}=\frac{2.2}{4}=.55=\)

55 percent

Answer D