You buy a lily and an African violet on the same day. You are instructed to water the lily every fourth day and to water the violet every seventh day after taking them home.
What is the first day on which you will water both plants on the same day? How can you use this answer to determine each of the next days you will water both plants on the same day?
Answer (3)
The "least common multiple" of 4 and 7 is 28. Beware of anybody who tells you to just multiply them. The least common multiple is not always their product. For example, the least common multiple of 4 and 6 is 12, NOT 24.
The correct answer is:
The 28th day, and every 28 days after.
Explanation :
We want to find the least common multiple (LCM) of 4 and 7 to solve this. To find the LCM, we find the prime factorization of each number:
4 = 2*2
7 = 1*7
We look for common factors; there are none. We multiply the uncommon factors (in this case, all of them): 2 2 7 = 28
This means the first day we water both is day 28. Every 28 days we will water both plants on the same day.
You will water both the lily and the African violet on the same day for the first time on day 28 and then every 28 days thereafter. This is calculated using the least common multiple of their watering schedules, which is 28. Thus, the subsequent days will be day 56, day 84, and so on.
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