Multiple-choice questions ask this quickly and I don't have time to compute percentages.
Accepted answer
Reason from the product's characteristics:
**More elastic** — many close substitutes, a luxury rather than a necessity, a large share of income, and a long time horizon to adjust. (A specific brand of cereal.)
**More inelastic** — few substitutes, a necessity, a small share of income, short time horizon, addictive or habitual. (Insulin, gasoline this week.)
The total-revenue test is the fastest shortcut when a price change is given: if price rises and total revenue **falls**, demand is elastic; if revenue **rises**, it's inelastic. And note that elasticity varies along a straight-line demand curve — elastic up top, inelastic at the bottom — so "the demand curve is elastic" is usually the wrong phrasing.