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Out of the 260 lunches, 19 of them could be expected to contain a ham sandwich with chips that are NOT plain potato chips.
5 (ham, barbecue chips) + 4 (ham, tortilla chips) = 9 lunches with ham and chips that are NOT plain
9/26 = X/260
26X = 2340
X = 90
90/260 = 0.34615384615
So, 0.34615384615 * 260 = 90 lunches out of 260 could be expected to contain a ham sandwich with chips that are NOT plain potato chips.