Donna You may find both answers are correct. It is the traders choice which strike they remove the conversion [-u +c -p] at in order to determine the synthetic equivalent. If you remove the conversion at the 70 strike; you get +70c / +70p / -80p If you remove the conversion at the 80 strike; you get +80c / +2 70p / -2 80p Have a go at putting all the positions in whatever analyser you use and see if there is any difference. Have a good weekend. James
Got it. You add an 80P to the stock and subtract it to form the spreads. I stand corrected. (see how easy it is) However, I don't think that the second more cumbersome synthesis would be the choice of very many traders.