Answer:
Step-by-step explanation:
<u>Formula</u> for calculating speed:
Therefore:
<u>Given values</u>:
- x = the current (in mph)
- Speed = 10 mph
- Distance = 21 miles
- Total time = 5 hours
If the boat is traveling downstream, the current (x mph) will be pushing the boat <u>faster</u>, and so the boat's speed will increase by x mph.
Therefore, the expression for the time it takes for the boat to travel downstream is:
If the boat is traveling upstream, the current (x mph) will be pushing <u>against</u> the boat and so the boat's speed will decrease by x mph.
Therefore, the expression for the time it takes for the boat to travel upstream is:
Therefore, if the total time it takes to travel downstream <em>and</em> upstream is 5 hours:
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<u>To solve for x</u>:
Therefore, the rate of the current is 4 mph.