In this Cyberchase video segment, Harry responds to a "Get Rich Quick" ad and finds himself selling Cheesy Greeting Cards. Unfortunately, he has trouble selling all of the cards to friends and relatives, so he sets up a stand on the sidewalk. When he uses a calculator to find the total amount of money he has collected, he is happy to learn it is over $250. But when he looks at the stack of unsold cards, he questions his calculation. He decides to check his total using estimation, and he soon realizes he had made an error on his calculator.
There are many instances in which it is helpful to estimate, or make a reasonable guess about a numerical value. Sometimes a value is just not known, as is the case with events happening in the future, so it may be necessary to predict by estimating. This is the case with predicting rainfall amounts or the total cost of an upcoming trip. In other cases, using estimation is helpful in doing quick mental calculations or checking an answer that you've already calculated.
When making estimates, it is useful to round numbers up or down to simplify calculations. When you round numbers, you add to or subtract from a number to reach a number that is easier to work with—perhaps a whole number or a multiple of ten, for example. The place value to which you round each number depends on the specific problem at hand and how good an estimate you need, but you should always round each number to the same place value. If you are dealing with money, sometimes it is easier to round to the nearest dollar. For example, if you are purchasing a shirt that costs $39.50 and you want to calculate how much it costs after applying a 25% discount, it's easier to estimate the cost by rounding the price up to $40 and taking 25% off of that.
A good estimate will always be reasonably close to the exact result, and you have control over how close it actually is. By selecting the place value to which you round, you can increase or decrease the accuracy of an estimate. For example, if you are adding 111.32 + 237.19 +156.98, a quick but less accurate estimate can be found by rounding to the nearest ten: 110 + 240 + 160 = 510. A more accurate estimate could be found by rounding to the nearest dollar: 111 + 237 + 157 = 505. And to get really close, you could round to the nearest ten cents: 111.30 + 237.20 + 157.00 = 505.50. Of course, this last estimate is very close to the actual answer and requires almost as much work as finding the actual sum, so it isn’t terribly helpful. But it all depends on how close you want your estimate to be. In this example, some numbers were rounded up and some were rounded down. But if you want to be sure that you overestimated the result (for instance, if you want to make sure you have enough money for a purchase), you would round each number up. On the other hand, rounding each number down will cause you to underestimate, which might be beneficial in some situations.
HARRY: And Captain Angelina wins another battle for humanity. She's my hero.
Magic shark’s teeth…Get rich quick.
I would so like to be rich.
Sell Cheesy Greeting cards to family and friends. Cards for every occasion. See fine print.
Sell each box of our fabulous greeting cards for nine dollars.. Minimum order three dozen boxes. That’s easy...I’ve got lots of relatives and loads of friends.
It won't be long now.
DELIVERY MAN: Harry Wilson?
DELIVERY MAN: Sign on line 15.
HARRY: Sure. 12, 24, 36. Happy Birthday, I hope you don't feel as old as you look. Sorry you're sick, did you get a shot? Roses are red, Violets are green, my face is funny, your's is a scream. Your friend. What kind of friend would send these cards?
Thanks, Aunt Olive May. I'll send the cards right out.
Let’s see, that’s cousin Shawna, Uncle Chuck, and Aunt Olive May. That leaves just a little under three dozen left to sell.
Cheesy Greeting Cards. Get your Cheesy Greeting Cards. Cheesy Greeting Cars. Cheesy Greeting Cards. Cheesy Greeting Cards!
Hey, when was the last time you sent your mom a card to say, “What’s cooking?” I’ve got cards.
Please buy my cards, someone buy my cards, please!!
No, no, yes, yes, no, no, yes, no. That's everybody in my address book.
27. 18. 9. 36. More than $250! Not bad.
Ahhhhggggggggg! It can't be. They must be breeding! Or, or maybe my addition was wrong? That can't be I used an adding machine.
I sold 10 boxes but if my total is more than $250, that would mean each box would have to cost about $25. That can't be right.
Let's see. 27 rounds up to 30, and 18 rounds up to 20, 9 rounds up to 10 and 36 to 40. 30+20 = 50. 50 +10 = 60, and 60+40 = 100! The total should be closer to 100 not 252.
Here’s my mistake. I punched in 180 instead of 18! Get rich quick ...in a few hundred years. I have a better idea.
Dear Aunt Cathy, I want to be the first one to wish you a happy birthday.
I know your birthday isn't for 5 months. My birthday is coming soon, too. I’ll never forget the skates you got me on my tenth birthday. Love, Harry
Won’t be long now.
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