Question Number 39640 by Rio Mike last updated on 09/Jul/18
$${John}'{s}\:{age}\:{is}\:\mathrm{3}{x}\:{years}\:\mathrm{3}\:{years} \\ $$$${after}\:{he}\:{was}\:\mathrm{27}\:{years}\:{old} \\ $$$${what}\:{was}\:{his}\:{age}\:\mathrm{3}\:{years}\:{before} \\ $$$${hence}\:{find}\:{the}\:{sum}\:{of}\:{the} \\ $$$${family}\:{ages}\:\underset{{x}=\mathrm{1}} {\overset{\mathrm{60}} {\sum}}\left(\mathrm{3}{x}\right)^{\mathrm{3}{x}−\mathrm{1}} \\ $$
Answered by $@ty@m last updated on 09/Jul/18
$$\mathrm{3}{x}+\mathrm{3}=\mathrm{27} \\ $$$$\Rightarrow{x}=\mathrm{8} \\ $$$$\therefore{John}'{s}\:{age}\:\mathrm{3}\:{yrs}\:{before}=\mathrm{21}\:{yrs}. \\ $$