"Let There Be Light!" |

Part I

One of the most important monthly bills that every family must pay is the "light" bill (or electricity bill). And if your family is like most, the amount is often a great surprise. It just seems to go up and up all the time.

Of course, CAESS explains that the reasons for their higher charges are based on many factors: destruction of power lines, cost of operations, expansion of services, etc.

Below is CAESS's own chart showing how they compute your bill. Let's use it, and your calculator, to figure out some problems about monthly bills.

RATE TABLE |
||

For the first | 40 KWH | each one costs ¢0.166 |

For the next | 160 KWH | each one costs ¢0.254 |

For the next | 300 KWH | each one costs ¢0.419 |

In excess of | 500 KWH | each one costs ¢0.738 |

José and Maria Sanchez have just recently moved into their new apartment. Since they've only been there for two weeks, they haven't had much time to use much electricity. So their bill said they had only consumed 256 KWH (kilowatt-hours). What should they have to pay?

**Solution:** Since they've used 56 KWH over the first 200 (40 + 160),
their bill will be figured this way:

a) 40 × 0.166 = 6.64 b) 160 × 0.254 = 40.64 c) 56 × 0.419 = 23.464 Total = 70.744 So, their bill is ¢70.74.

**Exercise Set I:** Compute the amount a person would have to pay for
these KWH figures.

1) 188 KWH 2) 349 KWH 3) 425 KWH 4) 580 KWH 5) 121 KWH 6) 1024 KWH

Part II

On the left side of a receipt there are two numbers. They tell the current and previous readings of the electrical usage in your house, as indicated by the electricity meter that is outside your house.

Below are given some possible readings that might have been done by CAESS's meter reader.

**Exercise Set II:** First find the number of kilowatt-hours consumed, then compute the bill.

Current Previous Total Amount reading reading used to pay 1) 2455 2266 ________ ________ 2) 4096 3725 ________ ________ 3) 8112 7616 ________ ________ 4) 11043 9648 ________ ________ 5) 13954 13427 ________ ________

Part III

The following "story problems" are examples of what you might expect to see in an algebra course. They are not exactly what you would see in "real life", so they could be considered as puzzle problems. But if you think carefully about how you worked the exercises in Sets I and II, you can do these as well.

**Exercise Set III:**

1) Saul paid his light bill yesterday. If he wrote a check for ¢101.75, what KWH number was on his bill? 2) Sandra says that when she paid her electricity bill today, she paid ¢20.95 more than did Saul. If this was true, what was the KWH value on her receipt? 3) Mario went to the bank to make a deposit in his savings account, while at the same time pay his light bill. He says he'll save gas and time if he does it that way. He pays the bank teller the sum of ¢78.29. How many kilowatt-hours of electricity did he use? 4) Marina also decided to "kill two birds with one stone" when she went to her savings and loan office to pay her mortgage payment on her house as well as take care of some "lighter" business. If she paid ¢114.74 to CAESS, how many KWHs did her bill show? 5) Edgar paid ¢166.27 for his bill this month. What number would he see for his current reading if the previous reading was 4853 KWH? 6) Elena had a ¢191.43 payment to make last month. What was the previous reading number on her receipt if the current reading was 9557 KWHJ. 7) Forgetful Fred always forgets where he keeps his important papers. His wife is constantly "getting on his case" about that (making his life miserable). He could not locate the June receipt, but knew that he had paid it because his check book stub showed an amount of ¢209.88. He did manage to locate his May receipt, which gave a current readig of 7642 KWH. Lucky for you because you must tell me what the current reading on the June receipt was. Can you? 8) Ask your parents if you may look at a recent light bill receipt to check out the computation made by CAESS. 9) Write up your own "light" story problem. Be as interesting and creative as you can. Be sure you can solve it, too. Then put it on a separate sheet of paper. (Type it if possible.) But one more thing: use a fake name instead of your own in the upper right corner of your paper. This is because some of the best ones will be used to form a quiz for you and your classmates. tt(8/7/90)

CAESS also included a large table of information in the brochure. This was an attempt, a feeble one in my humble opinion, to show the consuming public how dramatically one's bill increases depending on the various appliances used around the house. This table is presented below; you are invited to study it carefuly. How many errors or examples of illogical reasoning can you find in it? It seems to me to have been prepared by someone who didn't understand mathematics very well. (Of course, I doubt very many individuals who received the pamphlet even bothered to examine it at all. Or they just meekly nodded their heads and thought, "Gee! How expensive things are becoming!")

Typical Household Consumptionat current price rates |
|||||

Household appliance | Use kwh/mo. | Accumulated kwh | Monthly cost | Accumulated cost | Unit Cost |

6 light bulbs 60 w, 4 hr/da | 54 | 54 | 10.20 | . | 0.30 per day |

iron 1500 w, 6 hr/wk | 36 | 90 | 9.14 | . | 0.23 per hr |

refrigerator 250 w, full time | 60 | 150 | 15.24 | . | 0.51 per day |

television 250 w, 6 hr/da | 45 | 195 | 11.43 | . | 0.06 per hr |

radio, fan, blender (mo.) | 30 | 225 | 11.75 | . | 0.39 per day |

stereo 150 w, 4 hr/da | 18 | 243 | 7.54 | . | 0.06 per hr |

hair dryer 1500 w, 10 hr/mo | 15 | 258 | 6.29 | . | 6.29 per mo. |

Subtotal 1 | 258 | 258 | 71.58 | 71.58 | 2.39 per day |

stove, burners only 5000 w | 120 | 378 | 50.28 | . | 1.68 per day |

oven of stove 4000 w, 10 hr/mo | 32 | 410 | 13.41 | . | 0.56 per hr |

Subtotal 2 | 152 | 410 | 63.69 | 135.27 | 2.12 per day |

cistern motor 1/2 HP | 36 | 446 | 15.08 | . | 0.50 per day |

2nd TV | 30 | 476 | 12.57 | . | 0.07 per hr |

betamax | 20 | 496 | 8.38 | . | 0.28 per day |

Subtotal 3 | 86 | 496 | 36.03 | 171.30 | 1.20 per day |

6 additional light bulbs | 36 | 532 | 24.55 | . | 0.82 per day |

2 reflectors of 150 w | 27 | 559 | 19.93 | . | 0.66 per day |

water heater 1500 w, 3 hr/da | 90 | 649 | 66.42 | . | 2.21 per day |

3rd TV | 24 | 673 | 17.71 | . | 0.15 per hour |

Subtotal 4 | 177 | 673 | 128.61 | 299.92 | 4.29 per day |

air conditioner 18000 BTU 10 hr/da | 900 | . | 664.20 | . | 2.21 per hr |

TOTAL | . | 1573 | . | 964.12 | . |

As is so true in modern economies, prices usually go up in such businesses such as public utilities. This was true in this case anyway. Below is the rate table that came out about a year later.

It is certainly interesting to note two things here. (1) The public did not receive a brochure this time explaining the system or that a raise in rates even occurred. (2) Notice that in the first table the costs per KWH are "messy" 3-place decimal values, whereas in the second one they are more normal "money" style values. I have always wondered why this was done. But I never got around to asking that question.

RATE TABLE |
||

For the first | 40 KWH | each one costs ¢0.20 |

For the next | 160 KWH | each one costs ¢0.35 |

For the next | 300 KWH | each one costs ¢0.60 |

In excess of | 500 KWH | each one costs ¢0.75 |

A couple of interesting questions naturally arise as one contemplates the two rate tables. (1) What are the percent increases for each of the four levels of the chart? And (2) what is the percent increase on sample bills when the amount to pay is computed using the old rates vs. the new rates?

I wonder what the current rates are now in 1999?

Comments? Send e-mail. | Back to top | Go back to Home Page | Go back to Contents |