Karen packs peanut butter sandwiches in her daughter's lunch 2 randomly chosen days of the week. The other 3 school days, she packs a ham sandwich. She packs a piece of cake on one randomly chosen day and cookies the other four days. What is the probability, expressed as a percentage, that Karen packs a ham sandwich and cake on the same day?
Please reason step by step, and put your final answer within \boxed{}.
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