What are THREE GOODS for which the demand is inelastic, with respect to price? Do these goods ever go on sale? Does understanding the relationship between elasticity and total revenue help you understand why some goods go on sale, and others don't?

Goods can be price inelastic for more than one reason.

1) The first reason is that there's a limited quantity needed. Right now at my house, we need about half a dozen mousetraps because we live out in the country, and the mice will start trying to come in as the nights get colder. But that's as many as we can use - if they cost a dollar, we'll buy 6. If they cost five bucks, we'll still buy six. But we wouldn't need more, even if they were free.

2) The second reason is that the item is a small part of your budget. Salt and other spices are a good example here. Even if containers of salt and pepper go on sale at the supermarket, you probably wouldn't buy more than one extra, because you won't use it before it spoils, and you'll have to store it for quite a while. And they're not expensive, so you're likely to buy them as needed.

3) The third kind of inelastic demand is the one you're most likely to think of first - goods or services that are absolutely necessary. Electricity for your home and gasoline for your car are good examples. Although there are price changes, these two items really never go "on sale."

If the price rises substantially, and if you expect the price to stay high for a long time, you might rethink owning a car. But for the short run, you're likely to just pay the higher price and complain about the oil companies. Likewise, it would take a lot for electricity to be so expensive that you would consider figuring out a way to do without it.