In a certain month a baseball team that played 60 games had won 30\% of its games played. After a phenomenal winning streak this team raised its average to 50\%. How many games must the team have won in a row to attain this average?
(a)12
(b)20
(c)24
(d)30
Answer
Answer (as printed): C
Explanation
Number of games already won $=30 \%$ of $60=18$. Let the required number of games be $x$. Then, $$\begin{aligned} \frac{18+x}{60+x} \times 100=50 & \Rightarrow \frac{18+x}{60+x}=\frac{1}{2} \\ & \Rightarrow 36+2 x=60+x \Rightarrow x=24 . \end{aligned}$$
Explanation as extracted from the printed page; notation may be imperfect.