Question 1203109
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Tutor @josgarithmetic loves those magic formulas with lots of variables that you can use to solve a problem like this -- if you like magic formulas and don't care anything about learning HOW to solve the problem.<br>
Tutor Math_tutor2020 provides a valid algebraic solution but using a very slow method.<br>
Tutor @ikleyn uses a quick and easy method to solve the problem.<br>
Choose what fits your taste....<br>
And if formal algebra is not required, this is a common type of problem that can be solved quickly and easily using a bit of logical reasoning and simple arithmetic.<br>
Determine from the given information that the upstream speed is 12 km/hr and the downstream speed is 20 km/hr.<br>
Then use logical reasoning to find the answers.<br>
The 20 km/hr is the boat speed plus the current speed; the 12 km/hr is the boat speed minus the current speed.  Picture that on a number line -- you add the current speed to the boat speed and you get 20 km/hr; you subtract the current speed from the boat speed and you get 12 km/hr.<br>
That means the boat speed is halfway between 20 km/hr and 12 km/hr -- that is, 16 km/hr.  And then the current speed is the difference between 16 km/hr and either 20 km/hr or 12 km/hr -- that is, 4 km/hr.<br>
ANSWERS: boat speed 16 km/hr, current speed 4 km/hr<br>