The distance between two piers is S miles. Two boats started moving simultaneously at speeds R1 and R2. How can you find the distance D between them if they moved for T hours in opposite directions.

To find the distance D between the two boats after they have moved for T hours in opposite directions, we can use the formula:

D = |(R1 + R2) * T|

Here's how to get this answer:

1. Determine the total speed: Add the speeds of the two boats to find the total speed at which the distance between them is changing. This can be done by adding R1 and R2: R_total = R1 + R2.

2. Multiply the total speed by the time: Multiply the total speed (R_total) by the time (T) for which the boats have been moving. This will give you the distance covered by both boats in opposite directions: D = R_total * T.

3. Take the absolute value: Since the distance covered in opposite directions can be negative when the boats move in different directions, take the absolute value of D to get the positive distance between them: D = |R_total * T|.

Note: The absolute value |x| represents the positive value of x, regardless of its sign.

By following these steps, you can find the distance D between the two boats after they have moved for T hours in opposite directions.

distance = speed * time

their combined speed is R1+R2
So, D = S + (R1+R2)*T if they are moving away from each other.
So, what if they are approaching each other?