Which pencil is the longest 7 cm or 64 mm?

Well, isn't that just a happy little question! Let's see, to compare the lengths of the pencils, we need to make sure we're using the same units. Since 1 cm is equal to 10 mm, we can convert 7 cm to mm by multiplying it by 10. So, 7 cm is equal to 70 mm, making the pencil that is 64 mm long the shorter one.