A boat travels 7 kilometers upstream in 42 minutes. If the stream flows at a rate of 3 kilometers per hour, determine the speed of the boat in still water.

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First, you need to calculate the upstream speed of the boat.

The boat travels 7 km upstream in 42 minutes.
Converting this time to hours: 42 minutes = 42/60 = 0.7 hours

Upstream speed = Distance/Time = 7 km ÷ 0.7 hours = 10 km/hr

From the image, we can see that this calculation is correctly shown as:
Rate upstream = (7/42 × 60) kmph = 10 kmph

For boats and streams problems, we know that:
Upstream speed = Speed in still water - Stream speed

Therefore:
10 km/hr = Speed in still water - 3 km/hr
Speed in still water = 10 + 3 = 13 km/hr

The speed of the boat in still water is 13 km/hr.

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