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a-boy-rides-his-bicycle-10km-at-an-average-speed-of-12-km-hr-and-again-travel-12-km-at-an-average-speed-of-10-km-hr-his-average-speed-for-dntire-trip-is-approximately-a-10-4km-hr-b-10-8km-hr-c-12-2km




Question Number 32209 by Raja1 last updated on 21/Mar/18
a boy rides his bicycle 10km at an average speed of 12 km/hr.  and again travel 12 km at an average speed of 10 km/hr  his average speed for dntire trip is approximately  a)10.4km/hr  b)10.8km/hr  c)12.2km/hr  d)11.2km/hr
$${a}\:{boy}\:{rides}\:{his}\:{bicycle}\:\mathrm{10}{km}\:{at}\:{an}\:{average}\:{speed}\:{of}\:\mathrm{12}\:{km}/{hr}. \\ $$$${and}\:{again}\:{travel}\:\mathrm{12}\:{km}\:{at}\:{an}\:{average}\:{speed}\:{of}\:\mathrm{10}\:{km}/{hr} \\ $$$${his}\:{average}\:{speed}\:{for}\:{dntire}\:{trip}\:{is}\:{approximately} \\ $$$$\left.{a}\right)\mathrm{10}.\mathrm{4}{km}/{hr} \\ $$$$\left.{b}\right)\mathrm{10}.\mathrm{8}{km}/{hr} \\ $$$$\left.{c}\right)\mathrm{12}.\mathrm{2}{km}/{hr} \\ $$$$\left.{d}\right)\mathrm{11}.\mathrm{2}{km}/{hr} \\ $$
Answered by MJS last updated on 21/Mar/18
10km at 12km/hr ⇒ 5/6 hr  12km at 10km/hr ⇒ 6/5 hr  22km in 5/6+6/5=61/30hr ⇒  ⇒ 22×30/61≈10.8km/hr
$$\mathrm{10}{km}\:{at}\:\mathrm{12}{km}/{hr}\:\Rightarrow\:\mathrm{5}/\mathrm{6}\:{hr} \\ $$$$\mathrm{12}{km}\:{at}\:\mathrm{10}{km}/{hr}\:\Rightarrow\:\mathrm{6}/\mathrm{5}\:{hr} \\ $$$$\mathrm{22}{km}\:{in}\:\mathrm{5}/\mathrm{6}+\mathrm{6}/\mathrm{5}=\mathrm{61}/\mathrm{30}{hr}\:\Rightarrow \\ $$$$\Rightarrow\:\mathrm{22}×\mathrm{30}/\mathrm{61}\approx\mathrm{10}.\mathrm{8}{km}/{hr} \\ $$

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