Porisma

A hint to get started

Count the settings of a four-wheel lock

Do you know the total number of combinations possible on a combination lock which contains 4 wheels each numbered 0–9?

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Schematic of the source four-wheel lock: each labelled wheel can display a digit from zero to nine. Every wheel has ten choices, repetition is allowed, and leading zero is allowed.
Schematic of the source four-wheel lock: each labelled wheel can display a digit from zero to nine. Every wheel has ten choices, repetition is allowed, and leading zero is allowed.
Schematic of the source four-wheel lock: each labelled wheel can display a digit from zero to nine. Every wheel has ten choices, repetition is allowed, and leading zero is allowed.

CJC · Lecture · Opening lock question (unnumbered)

Decide whether order matters and repetition is allowed; then count stages or disjoint cases.

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