To find the decimal equivalence of the number of correct answers, you divide the number of correct answers by the total number of questions:
\[ \text{Decimal} = \frac{15}{20} = 0.75 \]
To find the percent equivalence, you multiply the decimal by 100:
\[ \text{Percent} = 0.75 \times 100 = 75% \]
So, Jackie answered 0.75 (or 75%) of the questions correctly.