Nhóm	$\left[ {50;60} \right)$	$\left[ {60;70} \right)$	$\left[ {70;80} \right)$	$\left[ {80;90} \right)$	$\left[ {90;100} \right)$
Tần số	$4$	$5$	$23$	$6$	$2$	$N = 40$