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