What is a 90-ball bingo strip?
A 90-ball bingo strip is a set of six tickets that between them contain every number from 1 to 90 exactly once, so every number called marks exactly one square somewhere on the strip.
Each ticket in the strip is a grid of nine columns by three rows — 27 squares, of which 15 hold numbers and 12 are left blank, five numbers to a row. Six tickets × 15 numbers = 90, which is why a full strip uses up the whole range with nothing repeated and nothing missing.
The columns are fixed ranges: the first column takes numbers 1 to 9, the next seven columns take 10–19, 20–29 and so on up to 70–79, and the last column takes 80 to 90. Numbers inside a column run downward in order.
Prizes in 90-ball are usually won in three stages on a single ticket: one line, then two lines, then a full house of all fifteen numbers. Buying a whole strip guarantees a mark on every call, which is why UK halls sell tickets in sixes.