Question

A submarine descends 15 meters every 3 minutes. Which expression represents its depth after 12 minutes?
A. 15 × 12 ÷ 3
C. −15 × 12 ÷ 3
B. 15 × 3 ÷ 12
D. −15 × 3 ÷ 1

Answer 1

To determine the depth of the submarine after 12 minutes, we first note how deep it descends:

The submarine descends 15 meters every 3 minutes.

First, let's find out how many 3-minute intervals are in 12 minutes:
\[
\frac{12 \text{ minutes}}{3 \text{ minutes}} = 4
\]
So, in 12 minutes, the submarine makes 4 descents.

Next, we can calculate the total descent after 12 minutes:
\[
\text{Total descent} = \text{Descent per interval} \times \text{Number of intervals} = 15 \text{ meters} \times 4 = 60 \text{ meters}
\]

Since the descent is in the negative direction (depth), we can represent it using a negative value:
\[
\text{Depth} = -60 \text{ meters}
\]

However, we need to express this in terms of the given options. We can also express the total descent in terms of the expression we need to evaluate:
\[
\text{Total descent} = -15 \text{ meters} \times \frac{12 \text{ minutes}}{3 \text{ minutes}} = -15 \times 4 = -60 \text{ meters}
\]

From the options provided, we can see:
- Option A: \(15 \times 12 \div 3\) calculates to 60, not considering the negative.
- Option B: \(15 \times 3 \div 12\) simplifies to \(3.75\).
- Option C: \(-15 \times 12 \div 3\) simplifies to \(-60\). (This is a correct match.)
- Option D: \(-15 \times 3\) gives \(-45\).

Thus, the correct expression that represents the submarine's depth after 12 minutes is:
**C. \(-15 \times 12 \div 3\)**.