Estimating for Everybody

Please see A World of Estimation

How many tons of apples does Bonavista make each year? Before you run off to the Internet, let me save you a LOT of time: Bonavista has NO apple industry at all. Furthermore you don’t need to know where Bonavista is or the size of the town or the climate, because you are going to be too busy calculating how many pears YOUR neighbourhood produces. Or how many berries; or how many daffodils. Or whatever suits your fancy.

I wanted to know the tonnage of apples produced each year in Bonavista, and since there is no apple-processor in town (indeed nothing within 500 Km for a crow, 23 hours driving for a human) so I had to do all the work myself.

The work is easy and, for me, fun. Remember “Management Measures”, and if you’re not managing, then your project is out of control.

There is a difference between guessing (or worse, reacting with “I have no idea”) and estimating. Estimating is a rational process. Guessing is staring at tea leaves.

(1) The population of Bonavista is 3,200 people. It isn’t 3,200 people, but:-

(a) I recall hearing six years ago that the population was 3,800, but at that time perhaps the speaker included Spillars Cove and Elliston.

(b) At least ten brick-and-mortar businesses have closed since then, so people have most likely moved away.

(c) 32 is an easy number to divide by 2 or by 4 and so on, so it lies on a nice boundary

(d) What is a definite lower-bound for the population of Bonavista? Well, one tenth of 3,200 is 320, and the population is significantly more than 300!

(e) What is a definite upper-bound for the population of Bonavista? Well, ten times 3,200 is 32,000, and the population is significantly less than 30,000!

(f) So my figure of 3,200 is based on something I heard, and is a better value than 320 and a better value than 32,000

(2) We can always go to the town hall and ask the true population of Bonavista, but whatever figure they give is will be better, because it is based on kept records, but it still won’t be accurate, because waddyaknow! Someone moved away yesterday and didn’t tell the town hall.

(3) So we will never have an up-to-the-minute value for the population; the best we can hope for is a “better figure”, never “the best”

(4) How many houses are there in Bonavista? Well, with a family of four in each house we expect about 800 houses.

(a) Again, there may be only 3 people per household, or only 2. But there are more than 0.4 people per household and less than 40 people living in any house in Bonavista, so we will go with 4. After all, 4 divides easily into 3,200

(5) So 800 houses in Bonavista. More than 80 at any rate, and less than 8,000.

(6) How many of these houses have an apple tree? I am tempted to say ten percent.

(a) One percent is too low and one hundred percent is known to be too high because I don’t have any apple trees on my lot.

(b) So we will start with a rational figure of ten percent.

(c) I can imagine my walk to the post office or to the supermarket and think of how many houses I pass, and how many of them are known to sport an apple tree

(7) If I have 800 houses and ten percent of them have one apple tree, then there are eighty apple trees in Bonavista.

(8) How many pounds of apples will a ten foot tree bear? (In Bonavista very few people prune their apple tree)

(a) A three-bushel sack of wheat weighs 180 pounds, so I will assume 200 pounds of apples per tree each year.

(9) Eighty apple trees at two hundred pounds of apples per tree yields 80 x 200 or 16,000 pounds of apples.

(10) Bonavista grows enough apples to be self-sufficient in pureed, bottles apple sauce. Some with a dash of cinnamon, some with a dash of nutmeg, but enough to supply both supermarkets.

How many tons of pears does Bonavista make each year?

How many tons of beets could Bonavista produce each year?

How many pumpkins could Bonavista produce each year?

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