அலைவெண் பரம்பல் — சா/த கணிதம்

Imagine a teacher marks 200 exam papers. Nobody wants to read 200 separate marks — what we really want to know is: how did the class do on the whole? Grouping those marks into bands like 50–59, 60–69 and counting how many fall in each is how real data — exam scores, heights of students, daily rainfall, factory output — gets tamed. Then, from that tidy table, we work out a single number, the mean, that summarises the lot. This is the everyday statistics that runs schools, shops and hospitals in Sri Lanka, and it is a reliable source of marks every O/L year.