每5个项目对数组中的项目进行分组，并在php中添加短划线

I'm building a loop that in my mind will output an array of items divided by a range of 5 numbers. I tried a few function like range, sort, implode, but I haven't found the right solution yet.

So far my code is the following:

foreach (range(0, 100, 5) as $number) {
  echo $number;
  print implode("-", str_split($number));
}

My goal is to output something like:

1-5
5-10
10-15

and so on that I can associate to anything, so essentially a range of numbers every a certain amount of numbers.

Plus I'm not sure if it's the right loop.

I guess I can obtain pretty much the same result with a for loop like:

for($i = 0; $i < 100; $i+=5)
{
     implode("-", str_split($i));
}

Where's my mistake?

UPDATE I probably forget to mention that everything is in a select item:

<select class="drops" name="largesan">
    <option selected value> -- How Many Sandwiches? -- </option><?php
    foreach (range(0, 100, 5) as $numbers)
    {
        $mynumber = $numbers . '-' . $numbers + 5;
        ?>
        <option value="<?php echo $numbers;?>"><?php echo $mynumber;?></option>
        <?php
    }
    ?>
</select>

You could use a foreach of this type

  foreach (range(0, 90, 5) as $number) {
    $myStr = $number . '-'. $number + 5 ;
    echo '<option value="'. $myStr .'">'. $myStr.'</option>' ;

  }

This is the code you should use ..

select class="drops" name="largesan"> 
  <option selected value> -- How Many Sandwiches? -- </option>
    <?php 
        foreach (range(0, 90, 5) as $number) { 

              $myStr = $number . '-'. $number + 5 ; 
              echo '<option value="'.  $myStr. '">'. $myStr .'</option>' ;
        }

     ?> 
 </select>

The answer in the select item is:

<select class="drops" name="largesan">
    <option selected value> -- How Many Sandwiches? -- </option><?php
    foreach (range(0, 95, 5) as $numbers)
    {
        $mynumber = $numbers . '-' . $numbers + 5;
        ?>
        <option value="<?php echo $mynumber;?>"><?php echo $numbers .'-'. $mynumber;?></option>
        <?php
    }
    ?>
</select>

Which means that a loop that prints a certain range of numbers, for example from 0 to 100 each, for another example, 5 numbers is the following:

foreach (range(0, 95, 5) as $numbers) {
$mynumber = $numbers . '-' . $numbers +5;
echo $numbers . '-' .mynumber;
}