Final answer:
It would take 7 people approximately 21.43 minutes to build the lego tower; hence the correct answer is 21 minutes (Option A). The problem is a work-rate scenario in Mathematics for Middle School, involving division and multiplication of person-minutes of work.
Step-by-step explanation:
The subject of this question is Mathematics, and it deals with the concept of work done by multiple people and how it scales with the number of people. The problem describes a work-rate scenario and asks how long it will take a different number of people to complete the same task.
Step-by-step explanation:
- First, we establish the total work done by 5 people in 30 minutes to build the lego tower. This can be considered as 5 people × 30 minutes = 150 person-minutes of work.
- Now, we need to find out how many minutes it would take 7 people to complete this 150 person-minutes of work. We divide the total work by the number of people: 150 person-minutes ÷ 7 people = approximately 21.43 minutes.
- Since none of the options matches 21.43 exactly, we round to the nearest option, which is 21 minutes (Option A).
Therefore, the correct answer is 21 minutes.
Review of addition of units of time:
- 15 minutes + 60 minutes = 75 minutes
- 10 minutes + 20 minutes = 30 minutes
- 15 seconds + 45 seconds = 60 seconds or 1 minute
Adding units of time is done by taking the sum of the given minutes or seconds separately and then, if necessary, converting them to higher units when the sum reaches the next threshold (60 seconds to a minute, 60 minutes to an hour).