A maths tutor in Cologne who teaches in English

import csv

with open("rad_koeln_2022.csv", encoding="utf-8") as sheet:
    rows = list(csv.reader(sheet, delimiter=";"))

counters = rows[0][1:]
january = rows[1]
print(counters[0], "in", january[0] + ":", float(january[1]))

Any percentage built on that number is wrong by a factor of a thousand, and nothing crashes to warn you. The fix is a small function that removes the thousands point before converting the text to a whole number. Version 2 uses it to add up each counter's year and to compare January with August.

def german_int(text):
    return int(text.replace(".", ""))

year = {}
for month in rows[1:]:
    for name, cell in zip(counters, month[1:]):
        year[name] = year.get(name, 0) + german_int(cell)

jan = german_int(rows[1][1])
aug = german_int(rows[8][1])
print(counters[0], "January:", jan, "August:", aug)
print(f"Change: {100 * (aug - jan) / jan:+.1f}%")
leader = max(year, key=year.get)
print("Busiest counter in 2022:", leader, year[leader])

Data: Stadt Köln, Fahrrad Verkehrsdaten Köln 2022 via Open.NRW, licence Datenlizenz Deutschland Zero 2.0, downloaded 3 November 2026. Year totals and changes are our own sums of the twelve monthly values.

One row breaks the pattern. At Universitätsstraße, August is lower than January, a fall of about 10 percent, while most counters rose sharply. The data does not explain it. A strong answer offers a hypothesis a pupil could test, for example the university's summer break, and says what other data would confirm or reject it.

1. Klasse 5 and 6. Hohenzollernbrücke shows 104.883 in August. Write it as an English number and round it to the nearest thousand. (Answer: 104,883; 105,000.)
2. Klasse 7. Universitätsstraße went from 110.382 in January to 99.332 in August. Work out the change in percent, to one decimal. (Answer: minus 10.0 percent.)
3. Klasse 8. For August, the mean of the 17 counters is 120,578.9 and the median is 113,372. Explain why the mean is higher. (Answer: two very busy counters, Venloer Straße and Deutzer Brücke, pull the mean up.)
4. Klasse 9 and 10. All counters together recorded 2,078,532 bikes in May and 1,020,325 in February. How many times as many is that? (Answer: about 2.04.)
5. Oberstufe. Write one sentence a ZP10 marker would accept for "Interpretiere den Wert 2,04 im Sachzusammenhang", and one that would lose the mark.

We wrote these tasks ourselves and checked every answer with our own runs on the city's file.