Answer:
19
Explanation:
Margin of Error (E) = t × sd/√n
√n = t ×sd/E
n = (t × sd/E)^2
Using a 90% confidence level, t = 1.645, sd = 2.9 inches, E = 1.1 inches
n = (1.645 × 2.9/1.1)^2 = 4.34^2 = 18.807
Minimum sample size required = 19 (to the nearest integer)