Limiting number of entries per column - Microsoft Community

hello,

as newbie, wondering if possible limit number of entries in column. please allow me explain needs.

the goal of spreadsheet teachers simultaneously  use office 365 assign students different activities without going on specified number of students per activity.

each column have name of activity such yoga or soccer or blocks. can accommodate number of students in each activity; yoga might limited 20, soccer 30, , blocks 40.

each teacher ask each student activity or wants , then, in same row student's name, enter x in appropriate column.

what need way disallow more entries column once maximum number of students per activity has been reached. example, once 20 students have signed yoga, column should not able accept more entries.

is possible and, if so, how can it?

thanks in advance can provide. i've looked through several articles, none seem address specific need. it's possible 1 might have, don't have expertise understand i'm looking at.

in gratitude,

laurie 

say column b has 1 activity in it. if put student limit in cell b1, use data validation in cells in column b with formula:

=(counta(b:b)-1)<=$b$1

and put message want pop when limit reached.

use same process other columns.

if have title in column or other entries in column, you'll need adjust 1 in formula appropriate number , not use cell b1 in formula, but use appropriate cell use enter limit. 

Office / Excel / Windows 8 / Office 365 for business