XED = -0.67
Working: XED = 4 ÷ (-6) = -0.67
Interpretation: XED = -0.67 → complements. Remember: Party Season Nearly Christmas — Positive substitutes, Negative complements.
XED mnemonic
Party Season Nearly Christmas — Positive substitutes, Negative complements. If XED > 0, goods are substitutes (e.g. butter and margarine). If XED < 0, complements (e.g. printers and ink).