Running at maximum speed, it takes a boat times as long to go 10 miles upstream as it does to go 10 miles downstream. if the current is 4 mph, find the speed of the boat in still water.

Note: The question states the time to go upstream is a number of times (not explicitly written) the time to go downstream. We'll assume a general number N

Explanation:

Relative Speed

If a boat is going upstream against the water current, the true speed of motion is , being the speed of the boat and the speed of the water. If the boat is going downstream, the true speed becomes .

The question states the time to go upstream is a number of times N (not explicitly written) the time to go downstream. The speed of an object is computed as

Where x is the distance traveled and t the time taken for that. The time can be computed by

If is the time for the upstream travel and is the time for the downstream travel, then

Siince the same distance x= 10 miles is traveled in both cases:

Simplifying and rearrangling

Operating

Solving for

If N=3

We can use the required value of N to compute the speed of the boat as explained

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