To convert the mixed number 1 1/3 to an improper fraction, follow these steps:
1. Multiply the whole number by the denominator of the fraction: 1 × 3 = 3.
2. Add the result to the numerator of the fraction: 3 + 1 = 4.
3. The improper fraction is the sum from step 2 over the original denominator: 4/3.
So, 1 1/3 as an improper fraction is 4/3.