time yourselfCostume 1 · weatherWed 7 October1 / 4
What is a "normal" (30-year average)?
"It was hot" said with numbers, not feelings. "Per one" appears too
Name Date
The 30-year normal, and the difference from itThe 30-year normal (called "heinenchi" in Japan) = the average over 30 years of a place's temperature or rainfall. Every 10 years it is renewed with a new 30-year span.
How far is this year from normal → difference = this year's value − the normal (+ means above normal, − below)
Say "it was hot" with a number, not a feeling.
The rule for this sheet (made up): a difference of +1.0 °C or more is "hot", −1.0 °C or less is "cool", anything between is "about normal".
| Town A | 2022 | 2023 | 2024 | 2025 | 2026 |
|---|
| August mean temperature (°C) | 27.9 | 28.3 | 27.2 | 26.8 | 28.9 |
Source: the August mean temperature of Town A (made up). The August normal of Town A is 27.4 °C.1 · The normal and the difference
1Over 30 years the August mean temperatures of Town A add up to 822.0 °C. What is the August normal?
2Find the difference for 2026 (28.9 °C). By the rule, is it "hot", "cool" or "about normal"?
3Find the difference for 2025 (26.8 °C). (It comes out negative.)
First, the most common mistake"The normal is a typical year, so most years land close to it." Not so.
The normal is an evened-out number. None of the five years in the table is exactly 27.4 °C. Years that match the normal can be the rare ones.
4Find the difference for each of the five years in the table. How many were above the normal?
5Find the mean of the five years, rounded to one decimal place. How many °C above (or below) the normal is it?
Work to two decimal places, then round.
6A friend called 2023 (28.3 °C) "hot". By this sheet's rule, what is it? Answer with numbers.
7In a town whose normal is 27.4 °C, one year had a difference of +2.1 °C. What was that year's mean temperature?
2 · Rainfall, and "per one"
8In August (31 days) this year Town A had 186 mm of rain. The August normal (made up) is 155 mm in total.
(1) How many mm per day this year? (2) How many mm per day is the normal?
(3) This year is how many times the normal?
| Daily highest temperature (°C) | 1 | 2 | 3 | 4 | 5 |
|---|
| Town P | 29.8 | 30.2 | 30.0 | 29.9 | 30.1 |
| Town Q | 24.5 | 35.5 | 30.0 | 33.0 | 27.0 |
Source: five days in one August (made up)9Find the mean of the five highest temperatures for Town P and for Town Q. Are they the same? Then find "the hottest day − the coolest day" for each.
10The normal is based on the total of 30 years. After 10 years the oldest 10 years are replaced by the newest 10.
The old 10 years total 273.0 °C and the new 10 years total 281.0 °C.
(1) Find the new 30-year normal, rounded to one decimal place. (The old 30-year total was 822.0 °C.)
(2) Find this year's difference for 28.9 °C against the new normal.
11Someone reasons: "Town A's August normal is 27.4 °C, so every August day is about 27 °C." Using question 9, write one thing an average alone cannot tell you.
12Looking only at the days it rained, what happens?
(1) In a normal August Town A has 9 rainy days and 155 mm in total. How many mm per rainy day? (Round to one decimal place.)
(2) This August it had 11 rainy days and 186 mm. How many mm per rainy day? (One decimal place again.)
(3) The total is bigger this year, yet what do (1) and (2) show when compared?
What "per one" means depends on what you count as one.