Priya covers a certain distance by her car at a speed of 21 km/h and returns at a speed of 17 km/h. What is her average speed during the travel?

$18\frac{15}{19}km/h$

Average Speed = \(\frac{2 × S1 × S2 }{S1 + S2}\)

= \(\frac{2 × 21 × 17 }{21+17}\)

= \(\frac{357 }{19}\)

= 18\(\frac{15 }{19}\)

So , the average speed during whole journey is 18\(\frac{15 }{19}\)