Jim and Hannah both want to buy a copy of book priced at EUR 25.

$jim_price = $hannah_price = Money::EUR(2500);

Jim has a coupon for EUR 5.

$coupon = Money::EUR(500);

Because $jim_price and $hannah_price are the same object, you’d expect Hannah to now have the reduced price as well. To prevent this problem, Money objects are immutable. With the code above, both $jim_price and $hannah_price are still EUR 25:

$jim_price->equals($hannah_price); // true

The correct way of doing operations is:

$jim_price = $jim_price->subtract($coupon);
$jim_price->lessThan($hannah_price); // true
$jim_price->equals(Money::EUR(2000)); // true