PHP logical operators and or

$a=10;
$b=11;
if($a==10 and $b==11)
{
echo $a+$b;

}

else {

echo $a-$b;   
}

21

------------

$a=10;
$b=111;
if($a==10 or $b==11)
{
echo $a+$b;

}

else {

echo $a-$b;


   
}

121