1. **Problem statement:** Gilberto and his two sisters have a total of 115 erasers. They want to divide these erasers equally among the three of them and give any leftover erasers to their mom. We need to find how many erasers the mom receives. 2. **Formula and rules:** When dividing a total number $T$ by a number of people $n$, the number of erasers each person gets is the quotient $q = \lfloor \frac{T}{n} \rfloor$, and the leftover (remainder) $r$ is given by $r = T - n \times q$ or simply $r = T \bmod n$. 3. **Apply the formula:** Here, $T = 115$ and $n = 3$. Calculate the quotient: $$q = \left\lfloor \frac{115}{3} \right\rfloor = \left\lfloor 38.333\ldots \right\rfloor = 38$$ Calculate the remainder: $$r = 115 - 3 \times 38 = 115 - 114 = 1$$ 4. **Interpretation:** Each sibling gets 38 erasers, and the leftover 1 eraser is given to their mom. **Final answer:** The mom receives **1** eraser. This corresponds to option A) 1.