A trade secret reveals why two packs of MM's weigh different amounts

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Quoctrung Bui/NPR

Note: This episode originally ran in 2014.

A few years ago, we noticed something strange: a pack of milk chocolate M&M's weighs 1.69 ounces, but a pack of peanut butter M&M's weigh a tiny tiny bit less, 1.63 ounces. The two packs are the same price, but you get slightly less of the peanut butter M&M's! 0.06 ounces less! It turns out there is a whole weird world living down there at the third decimal place. When you pull on that little thread, lots of things start to unravel.

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