https://ironscripter.us/a-powershell-counting-challenge/

PowerShellCounting.ps1

#region Beginner

<#
The challenge is simple: get the sum of the even numbers between 1 and 100. 
You should be able to do this in at least 3 different ways. Show all 3 ways. You don’t need to write any functions or scripts.
#>

# Method 1, foreach loop
$sum = 0
foreach ($n in 1..100) {
  if($n %2 -eq 0){
    $sum = $sum + $n
  }
}
$sum

# Method 2, while loop
$i = 0
$sum = 0
while ($i -lt 101) {
  if($i %2 -eq 0)
  {
    $sum = $sum + $i
  }
  $i++
}
$sum

# Method 3, PowerShell pipeline with ForEach-Object cmdlet
1..100 | ForEach-Object {if($_ %2 -eq 0){ $_ }} | Measure-Object -Sum | Select-Object -Property sum

#endregion

#region Intermediate

<#
After you’ve solved the beginner level, take what you’ve learned and create a PowerShell function to get the sum and 
average of every X number between 1 and a user specified maximum. 
For example, the function should produce a result that shows the sum and average of every 4th number between 1 and 512.
#>

function Get-Number {
  [CmdletBinding()]
  param (
      [Parameter(Mandatory)]
      [Int]
      $Max,
      [Parameter(Mandatory)]
      [Int]
      $Interval
  )
  Write-Verbose $Max
  Write-Verbose $Interval

  $numList = [system.collections.generic.list[int]]::new()

  for ($i = 1; $i -lt $Max; $i = $i + $Interval) {
    $numList.add($i)
  }
  $numList | Measure-Object -Average -Sum | Select-Object -Property Average, Sum
}
#endregion

#region Bonus Challenge
<#
If you want a bit more challenge add the following features to your function.

    Limit the interval to a value between 1 and 10
    Add a property to your output that includes all the matching number
    Let the user specify the starting and stopping numbers
#>

function Get-NumberBonus {
  [CmdletBinding()]
  param (
    # The minimum number to start from. Must be less the the max number value.
    [Parameter(Mandatory)]
    [ValidateNotNullOrEmpty()]
    [Int]
    $Min,
    # The maximum number where to stop. Must be greater that the min value.
    [Parameter(Mandatory)]
    [Int]
    $Max,
    # The interval to increment by. Between 1 and 10
    [Parameter(Mandatory)]
    [ValidateRange(1,10)]
    [Int]
    $Interval
  )
  Write-Verbose $Max
  Write-Verbose $Interval
  
  if($Min -ge $Max){
    throw 'Min cannot be equal or greater than Max'
  }

  $numList = [system.collections.generic.list[int]]::new()

  for ($i = $Min; $i -lt $Max; $i = $i + $Interval) {
    $numList.add($i)
  }

  $result = [PSCustomObject]@{
    'Average' = ($numList | Measure-Object -Average).Average
    'Sum' = ($numList | Measure-Object -Sum).Sum
    'MatchedNumbers' = $numList
  }
  $result
}
#endregion