So a midpoint multi would be 2.34 but the russos did civil war and that had a multi on memorial day of 2.11x so I don't think there's any certainty that IW will have stronger legs than Ultron, especially with han solo opening on that 4th weekend.
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All in all IW probably needs to open to over 210 to get to 500m by Memday, and maybe even as high as 235.