Final answer:
To find the number of days it takes for there to be 3 bottles left, we set up the equation 15 - 2d = 3 and solve for d. The result is d = 6, so it takes 6 days.
Step-by-step explanation:
We can solve this problem by setting up an equation using the given information.
Let d represent the number of days it takes for the student to reach 3 bottles.
We start with 15 bottles and drink 2 bottles each day, so the equation is: 15 - 2d = 3
To solve for d, we isolate the variable by subtracting 15 from both sides: -2d = -12.
Finally, we divide both sides by -2 to solve for d: d = -12 / -2 = 6.
Therefore, it takes 6 days for there to be 3 bottles left.