Question Number 39727 by Rio Mike last updated on 10/Jul/18
$${If}\:{the}\:{average}\:{of}\:\mathrm{4}\:{kids}\:{age}\:{is} \\ $$$$\mathrm{3}{c}\:{and}\:{the}\:{average}\:{of}\:{two}\: \\ $$$${of}\:{them}\:{is}\:\mathrm{33}.\:{find}\:{the}\:{value} \\ $$$${of}\:{c}. \\ $$
Commented by MrW3 last updated on 10/Jul/18
$${when}\:{the}\:{average}\:{age}\:{of}\:{two}\:{kids}\:{is} \\ $$$$\mathrm{33},\:{I}\:{think}\:{at}\:{least}\:{one}\:{of}\:{them}\:{is} \\ $$$${no}\:{kid}\:{any}\:{more}.\:{or}\:{have}\:{you}\:{ever}\:{seen}\:{two}\:\mathrm{33}\:{years} \\ $$$${old}\:{kids}\:{in}\:{your}\:{school}?\:\:{so}\:{I}\:{don}'{t}\:{treat}\:{them} \\ $$$${as}\:{kids},\:{but}\:{as}\:{persions}. \\ $$$${average}\:{age}\:{of}\:\mathrm{4}\:{persons}\:{is}\:\mathrm{3}{c},\:{it} \\ $$$${means}\:{the}\:{sum}\:{of}\:{their}\:{ages}\:{is} \\ $$$$\mathrm{12}{c}.\:{since}\:{two}\:{of}\:{them}\:{have}\:{a}\:{total} \\ $$$${age}\:{of}\:\mathrm{66}.\:{the}\:{total}\:{age}\:{of}\:{the}\:{other} \\ $$$${two}\:{persons}\:{is}\:\mathrm{12}{c}−\mathrm{66}.\:{let}'{s}\:{assume} \\ $$$${these}\:{persons}\:{are}\:{no}\:{babys}\:{more},\:{i}.{e}. \\ $$$${each}\:{is}\:{at}\:{least}\:{one}\:{year}\:{old},\:{then}\:{we} \\ $$$${have}\:\mathrm{12}{c}−\mathrm{66}\geqslant\mathrm{2} \\ $$$$\Rightarrow{c}\geqslant\frac{\mathrm{68}}{\mathrm{12}}=\frac{\mathrm{17}}{\mathrm{3}}\approx\mathrm{5}.\mathrm{7} \\ $$$${if}\:{c}\:{should}\:{be}\:{integer},\:{then}\:{c}\geqslant\mathrm{6}. \\ $$$${in}\:{general}\:{the}\:{most}\:{people}\:{can}\:{not}\:{be} \\ $$$${more}\:{than}\:\mathrm{100}\:{years}\:{old},\:{then}\:{we} \\ $$$${have}\:\mathrm{12}{c}−\mathrm{66}\leqslant\mathrm{200} \\ $$$$\Rightarrow{c}\leqslant\frac{\mathrm{266}}{\mathrm{12}}=\frac{\mathrm{133}}{\mathrm{6}}\approx\mathrm{22}.\mathrm{2} \\ $$$${so}\:{with}\:{normal}\:{human}\:{understanding} \\ $$$${the}\:{value}\:{of}\:{c}\:{should}\:{be}\:{between}\:\mathrm{6} \\ $$$${and}\:\mathrm{22}: \\ $$$${i}.{e}.:\:\mathrm{6}\leqslant{c}\leqslant\mathrm{22} \\ $$