the biology class has a lab every days. the earth science class has a lab every three days . which class day do they both have class ?

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To determine which day both classes have a lab, we need to find a common multiple between the number of days biology class has a lab (every day) and the number of days earth science class has a lab (every three days).

The multiples of "every day" would be: 1, 2, 3, 4, 5, ...

The multiples of "every three days" would be: 3, 6, 9, 12, ...

From the lists above, we can see that the first common multiple for both classes is 3. This means that both classes will have a lab on the 3rd day.

Therefore, the day when both classes have a lab is the 3rd day.