A car company sold 150 cars in a special 6-day sale. Each day, the company sold 6 more than the previous day. How many cars were sold on the 6th day?
(a)35
(b)40
(c)50
(d)60
(e)70
Answer
Answer (as printed): B
Explanation
Let the number of cars sold on the first day be $x$. Then, $x+(x+6)+(x+12)+(x+18)+(x+24)$ $$\begin{aligned} & +(x+30)=150 \\ & \quad \Leftrightarrow 6 x+90=150 \Leftrightarrow 6 x=60 \Leftrightarrow x=10 . \\ & \therefore \quad \text { Number of cars sold on } 6 \text { th day }=(10+30)=40 . \end{aligned}$$
Explanation as extracted from the printed page; notation may be imperfect.