Post amount must be in increments of 50 PHP : <p>i collect data using GET.</p>

<pre><code>product=shoes&amp;amount=30
</code></pre>

<p>so i collect the data</p>

<pre><code>$amount = $_GET['amount'];
</code></pre>

<p>How do i echo out a message if the amount is not in increments of 10, so for example if amount was 25, i want to echo out saying "Amount needs to be in increments of 10".
I have no code examples as i have tried to google this and can't find anything and i don't know where to even begin.</p>

<p>So i have not tried anything.</p>
