The factory is a row of machines that pass their parts along a conveyor belt. Every machine handles a fixed number per minute: the press makes 4 gears, the assembly uses 6.
The factory runs smoothly when every stage handles the same number of parts per minute. Then nothing piles up on the belt and no machine waits. That takes several machines of each kind.
Write the lists down: presses handle 4, 8, 12 ... assemblies handle 6, 12 ... Both lists meet at 12: 3 presses and 2 assemblies. This number is called the least common multiple.
For parents
What does this exercise practice?
The times tables are put to use here before they get a name: whoever lays the 4s and the 6s side by side finds the least common multiple on their own. This is the groundwork for finding common denominators later.
Common pitfalls
A common slip is mixing up the number of machines and the number of parts: the boxes on the left take how many machines there are, the box on the far right takes how many parts per minute. Whoever works out 4 × 6 = 24 finds a factory that also runs, but twice as big as needed. The smallest one is wanted.
How to practice at home
Two children walk along a chalk line side by side: one in steps of 4, the other in steps of 6. Where do their footprints meet? Each of those places is a common multiple.
Related: Number Sequence, Table of Values