To find the empirical probability of David's incorrect responses, we first need to determine how many items he got incorrect.
David got 45 out of 70 items correct. Therefore, the number of incorrect responses is:
\[ 70 - 45 = 25 \]
Now, we can find the probability of getting an incorrect response by dividing the number of incorrect responses by the total number of responses:
\[ \text{Probability of incorrect responses} = \frac{\text{Number of incorrect responses}}{\text{Total number of responses}} = \frac{25}{70} \]
Next, we simplify this fraction:
Both 25 and 70 can be divided by 5:
\[ \frac{25 \div 5}{70 \div 5} = \frac{5}{14} \]
Thus, the empirical probability of David's incorrect responses is:
\[ \frac{5}{14} \]