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13. Cross-price elasticity of demand is used to decide whether A. two commodities are substitutes or complements B. a product is a normal or a luxury good C. the demand is elastic of inelastic when price of the good itself changes D. the demand is popular or unpopular 14. Total utility is maximum when marginal utility is A. positive B. zero C. maximum D. negative 15. Which of the following statements is correct? A. the indifference curve is upwards sloping B. the indifference curve is convex to the origin C. if an indifference curve touches the Y-axis or X-axis, this means utility is maximum D. an Indifference curve may intersect with other indifference curves