They should be introduced in a positive manner, but they are likely to be done only if the extrinisic reward is desired and attainable. This is a really strange story. It's written in the first person, so that the person talking is the one who wrote the story about his experience. It has some pretty interesting words in it. They are on the board.
Banks use it for interest loans, and so on.
You're going to need to know fractions for math next year. You will need fractions in the world to come. Extrinsic rewards should be used only as necessary and should be withdrawn in a steady fashion over the time that the topic or unit is covered. Students should also see some relatively immediate use of the information and skills being learned. If possible use these tasks in the future as extrinsic rewards for less enjoyable tasks.