A person travels from P to Q at the speed of 20 km/h , from Q to R at 25 km/h, and from R to Z at 50 km/h .  If PQ = QR = RZ , then find the person's average speed ( in km/h ) .

\(\frac{300}{11}\)

Let , PQ = QR = RZ = x

Total Distance = 3x 

Distance = Speed ×  Time

Total Time = \(\frac{x}{20}\) + \(\frac{x}{25}\) + \(\frac{x}{50}\)

               = \(\frac{11x}{100}\)

Average Speed = \(\frac{Total\; Distance }{Total\;Time}\)

                     = \(\frac{3x\;×\;100 }{11x}\)

                     =  \(\frac{3\; × \;100}{11}\) = \(\frac{300}{11}\)