To calculate the score for a baby that is 18 inches long, we first determine how far it is from the reference point of 20 inches.
The difference is: 20 inches - 18 inches = 2 inches.
Since the baby is shorter than the reference point, the score will be negative.
Based on the given information, we can see that for every inch away from 20 inches, the baby receives a corresponding score adjustment. For the purpose of this calculation, we can interpolate between the examples provided (21 inches getting +1 and 16 inches getting -4).
- A baby at 21 inches (1 inch above reference) gets +1.
- A baby at 16 inches (4 inches below reference) gets -4.
This means that the score changes by 1 point for each inch above the reference and by roughly 0.75 points for each inch below the reference (since going from 20 to 16 is a total decrease of 5 points over a distance of 4 inches).
However, we have a baby that is 2 inches below 20 inches.
Calculating the score for 18 inches based on the previous results:
- If 16 inches is -4, and for every inch above the reference increases the score, an additional 2 inches above 16 inches would add +1.5 (since it is 2 inches higher than 16 inches).
- Thus, -4 + 1.5 = -2.5.
However, since we are dealing with whole numbers in the scores provided, we follow a simpler linear function based on the reference point:
For the simplest adjustment, we can align it as:
- 20 inches = 0;
- 19 inches = -0.5;
- 18 inches would then logically be -1.
Therefore, a baby that is 18 inches long receives a score of -1.
Final answer: -1