#! perl -slw
use strict;

my %table;
my $n=0;
for my $c ('A' .. 'Z') {
	$table{ +sprintf '%s%03d', $c, ++$n } = int(10+rand 100);
}

my $allocated = 0;
for my $school (sort keys %table) {
	my $needed = $table{$school};
	next if $allocated + $needed > 400;
	print "$school:$needed";
	last if ($allocated += $needed) >= 400;
}
print 'Total allocated: ', $allocated;

__DATA__
c:\test>226210
A001:107
B002:72
C003:15
D004:59
E005:106
O015:34
Total allocated: 393