Answer
Income elasticity of demand is not the same at all three prices.
Golf is not an inferior good, it is a normal good.
Work Step by Step
Formula for income elasticity of demand is:
Percentage change in quantity demanded of good/percentage change in income
At 50 dollars,
$\frac{50000-70000}{50000}$ ÷ $\frac{10-15}{10}$ = 0.80
At 35 dollars,
$\frac{50000-70000}{50000}$ ÷ $\frac{15-30}{15}$ = 0.40
At 20 dollars,
$\frac{50000-70000}{50000}$ ÷ $\frac{20-50}{20}$ = 0.27
Golf is not an inferior good as quantity demanded of gold increases when income increases, and thus it is a normal good.
