Both questions in this post are official ones sourced from The College Board’s question of the day app.

#### 1. October 31st, 2015

A) The number of neurons decreases by a fixed amount every 4 months.

B) The number of neurons remaining increases by a fixed amount every 4 months.

C) The number of neurons decreases by an amount proportional to the decrease in the previous 4 months.

D) The number of neurons increases by an amount proportional to the increase in the previous 4 months.

The best way to interpret this problem clearly is to make up some numbers.

Let \(r = 0.50\).

When \(t = 4\), \(N(4) = N_0(0.50)^1 = N_0(0.50)\)

When \(t = 8\), \(N(8) = N_0(0.50)^2 = N_0(0.50)(0.50)\)

When \(t = 12\), \(N(12) = N_0(0.50)^3 = N_0(0.50)(0.50)(0.50)\)

As you can see, the number of neurons is halved every 4 months. So if we start out with 100 neurons, the number will drop to 50 after four months, and then 25 after another four months.

Answers (B) and (D) are clearly wrong because the number of neurons doesn’t increase; it decreases. Answer (A) is wrong because the number of neurons does not decrease by a fixed amount every 4 months.

The answer is **C**.

#### 2. January 11th, 2016

(\(\text{revenue} = \text{price of product} \cdot \text{ number of products sold}\))

A) \(R(p) = 24,627(287 – 952p)\)

B) \(R(p) = 1,000(24,627 – p)(287 + 48p)\)

C) \(R(p) = (24,627 – p)(287 + p)\)

D) \(R(p) = (24,627 – 1,000p)(287 + 48p)\)

After \(p\) price reductions of \$1,000 each, the average price of an electric vehicle will be \(24,627 – 1,000p\) and the monthly purchases of electric vehicles will be \(287 + 48p\). Using the formula given in the question,

\[\text{revenue} = \text{price of product} \cdot \text{ number of products sold}\] \[R(p) = (24,627 – 1,000p)(287 + 48p)\]

The answer is **D**.

Do you have a recommended book for SAT Math 2 Subject?