Betty Robinson decided it was time for a change. She had been a social worker for

$10$ years, and although she found the work rewarding, it was time for something else.

So$,$ when Herbie's Hut came up for sale, she made some inquiries.

Herbie's Hut was a small gift shop and toy store in her old neighborhood of Skokie,

a Chicago suburb. Herb Gold had been running the business for $40$ years, but it was

a demanding job and he decided it was time to hang it up$.$ The business was pretty

steady, so Herb figured that there would buyers. He was delighted to hear from Betty,

whom he had known as a child growing up in the neighborhood. The money was less

important to Herb than making sure the store was in good hands. He had a good feeling

about Betty, so he agreed to let the business go for a modest price.

After Betty purchased the business, she decided to remodel the store. Herbie's Hut

would reopen as Betty's Best. Skylights, new wallpaper, and a fresh layout gave the store

a sprightlier look that reflected Betty's personality. During this time, Betty took a careful

look at the stock that came with the purchase. She noticed that several items were severely

understocked. Two of those were ID bracelets and Lego sets. She spoke with Herb about it

and he apologized. These were popular items and he hadn't had a chance to reorder them.

Betty was concerned that she might run out of these items quickly and that it would

hurt her reputation. When she called the suppliers she realized that she had no idea how

much to order. She asked Herb and he said that his rule of thumb was to order about one

month's supply. This sounded reasonable to Betty; she could figure out what a month's

supply was from the store's sales records, which Herb graciously turned over to her.

The store stocked hundreds of different items. It occurred to Betty that if she reor$-$

dered every item monthly, she would be spending a lot of time processing orders. Betty

thought that perhaps there was a better way. She consulted her boyfriend Bob who had