Grocery shopping, onions and waste

I took Belladonna back to school yesterday.  We swung by a grocery store on the way there. 

While in the produce department, she asked, "Which bag of onions should I get?"

I told her to pick the bag with the largest onions in it.

She asked "Why?"

I told her that there is less waste with larger onions.

But is it true?

I think it is true from a couple of different standpoints.  It takes more time to peel and chop small onions than to peel and chop large onions.  Not on a per-onion basis, but on a per-unit of chopped onions.

The average width of the seven outer layers was 3.5mm (0.140 inches)

The other source of waste relates to the fact that one often discards the outer-most layer...even though it is mostly good.

Horizontal axis is "Inches diameter".  Vertical axis is Percent waste.  Outer layer assumed to be 0.140" thick.

It is heartening to know that there are still things I can teach her.  And she listens!