Final answer:
The problem is a simple division of $10 among 3 sisters, resulting in each sister having an extra $3.33 to spend, in addition to their original $10, leading to $13.33 for each of the other sisters to spend.
Step-by-step explanation:
If there are 4 sisters each with $10.00, the total amount of money they have together is 4 times $10, which equals $40. Now, if one of the sisters decides she isn't feeling well and only wants a Sprite, her share of the money is given up to the others. Assuming the cost of a Sprite is negligible, or she pays for it from her own share, then the remaining $10 would be divided among the other three sisters.
To find out how much additional money each of the other sisters would have to spend, you divide the volunteered $10 by the 3 remaining sisters, which yields approximately $3.33 for each sister. Therefore, besides their original $10, each of the other sisters would now have an additional $3.33 to spend, making their total $13.33 each to spend.