To arrange the friends in order from least to greatest based on the amount of money they have saved, we look at their amounts:
- Charlotte: $38.91
- Celeste: $41.68
- Sami: $41.79
Ordering these amounts from least to greatest gives us:
- Charlotte: $38.91
- Celeste: $41.68
- Sami: $41.79
Therefore, the correct order from least amount saved to greatest is:
Charlotte, Celeste, Sami
So the correct answer is: Charlotte, Celeste, Sami.