If Janelle and three of her friends bought four smoothies of equal cost for a total of $4, it means that each smoothie cost $1 ($4 divided by 4).
If Janelle purchases the same smoothies for herself and nine of her friends, there would be a total of 10 people. Since each smoothie costs $1, Janelle would spend $1 per smoothie multiplied by 10 smoothies, resulting in a total expenditure of $10.
Therefore, Janelle would spend $10 if she purchases the same smoothies for herself and nine of her friends.
