To find the fraction \( u \) such that \( \frac{3}{8} \div u = \frac{10}{10} \), we can rewrite the equation as:
\[ \frac{3}{8} = u \cdot 1 \]
So we need to isolate \( u \):
- We know that dividing by a fraction is the same as multiplying by its reciprocal. Therefore, we can rewrite the division:
\[ \frac{3}{8} \div u = \frac{10}{10} \]
which means:
\[ \frac{3}{8} = u \cdot 1 \]
Thus, we can set up the equation:
\[ u = \frac{3}{8} \]
In conclusion, \( u \) is equal to \( \frac{3}{8} \).