Mrs.SImpson waters her geraniums once every 3 days, and she waters her other house plants once a week. How often does mrs.Simpson water all the plants on the same day?

Answer:She often waters all the plants on the same day every 21 daysStep-by-step explanation:- Mrs.Simpson waters her geraniums once every 3 days- She waters her other house plants once a week∵ Each week has 7 days∴ She waters her other house plants once every 7 days- We need to know How often does Mrs.Simpson water all the plants   on the same day* Lets think about that:∵ She waters her geraniums once every 3 days- That mean 3 , 6 , 9 , 12 , .............∴ She will water her geraniums in a multiple of 3∵ She waters her other house plants once every 7 days- That mean 7 , 14 , 21 , 28 , ................∴ She will water other house plants in a multiple of 7- That means she will water both in a common multiples of 3 and 7∴ She will water all in a common multiple of 3 and 7∵ The first common multiple of 3 and 7 is 21∴ Mrs.Simpson waters all the plants on the same day every 21 days* She often waters all the plants on the same day every 21 days