Final answer:
The coefficient of elasticity when the price increases from $5 to $6 and the quantity demanded decreases from 15 to 10 can be calculated using the midpoint formula and is found to be -1, showing unit elastic demand.
Step-by-step explanation:
To calculate the coefficient of elasticity when the price rises from P=$5 to P1=$6, and the quantity demanded decreases from Q=15 to Q1=10, we can use the midpoint formula for elasticity, which is (Q1 - Q) / [(Q1 + Q) / 2] divided by (P1 - P) / [(P1 + P) / 2]. Plugging in the numbers, we get elasticity = (10 - 15) / [(10 + 15) / 2] divided by (6 - 5) / [(6 + 5) / 2], which calculates to -1. Therefore, the coefficient of elasticity equals -1, indicating the demand is unit elastic.