Problem: Article: In the examples above, we've been dealing with a simplified market model that considers only one company without competition (a monopoly). More commonly, companies are under pressure to keep prices low due to competition. Under perfect competition, marginal revenue doesn't change as a result of the number of products sold, because prices are fixed. For instance, let's say that Kim's, the soda company from the examples above, is now in competition with hundreds of other soda firms. The price per can is set at $0.50 — any lower and Kim's will lose money, and any higher and customers will choose other products. Marginal revenue is always $0.50, since Kim's cannot sell cans for any other price. In real life, the small, competing firms that make up highly competitive markets aren't perfect. They don't instantly react to each others' price changes, they don't have perfect knowledge of their competition, and they don't always set their prices for maximum profitability. This sort of market system is called "monopolistic competition." Marginal revenue will typically decrease with each additional product sold, but not as steeply as it would in a monopoly. For example, Kim's drops the price of its soda from $1 to $0.85. It may still receive additional revenue, but in a monopolistic market, customers will still buy their competitors' soda for a higher price. In an oligopoly, a few large firms that are in competition with each other control the market. Marginal revenue usually has a downward trend with each additional unit sold, as it would in a monopoly. However, in real life, firms in an oligopoly are often reluctant to lower prices because it can result in a price-dropping war, reducing profits for all. Often, firms in an oligopoly will only lower their prices to force a small competitor out of business, then raise prices together to increase profitability for all. If firms in an oligopoly have agreed to set prices like this, sales levels depend on marketing and other considerations, not on price. Kim's has become a major soda player and now shares the market with Linda's and Andy's, two other soda firms. The three firms agree to sell their sodas at the same price, so marginal revenue for each additional soda will remain unchanged regardless of the price level they chose. If Jeff starts a small firm to undercut their inflated price, the three large firms may drop their prices so low that Jeff is forced out of business. The firms accept the reduced marginal revenue temporarily because they can raise the prices again once Jeff's is gone.
Summary: Understand marginal revenue under perfect competition. Know the behavior of marginal revenue under monopolistic competition. Know the behavior of marginal revenue under an oligopoly.

Problem: Article: After your surgery, you’ll need to learn how to walk on your repaired hip. You’ll also want to build up your strength and balance to protect yourself in the future. A physical therapist can help you reach your goals in a healthy and personalized manner.  Plan to continue physical therapy for up to three months.  During intensive physical therapy, you may need to attend sessions three or more times per week. Your physical therapist will likely recommend strength training and balance-building exercises to help you build your strength and recover. In addition to helping you feel better, these exercises will also help prevent future issues. Talk to your physical therapist about whether or not you’re ready for weight-bearing exercises. While being on your feet with activities such as walking will help you recover faster, if you aren’t ready it could set back your recovery. If that is your situation, your physical therapist may recommend starting with non-weight-bearing activities.  A great weight-bearing exercise for recovery is walking, either normally or on a treadmill. Non-weight-bearing exercises include activities like swimming or cycling.
Summary: Work with a trained physical therapist. Rebuild your strength and range of motion. Ask which type of exercise fits your needs.

Problem: Article: Flat irons with ceramic plates are much better for your hair, causing less damage while straightening more efficiently. Check to see if your flat iron has a ceramic plate, and if not, consider investing in one that does.
Summary:
Opt for a ceramic-plated flat iron.