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Medium size fruit

I need help determining what a medium size apple and banana are. I looked it up and I found information that said a medium size banana was about 7 inch long and a medium sized apple is about 2 3/4 inches in diameter. Does this sound right in everyone's experience. Also, potatoes. When thay say big, medium, small do they mean rusit potatoes? Because a small potatoe could be one of those really small ones so, I'm a bit confused. Thank you for your help!

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