Basic unitary method (constant rate): If 7 spiders make 7 webs in 7 days, how many days does 1 spider need to make 1 web?

Introduction / Context:
This is a direct unitary-method question. If multiple identical workers complete a proportional number of identical tasks in a given time, the rate per worker per day can be extracted and used to answer any equivalent scaling question.

Given Data / Assumptions:

• 7 spiders produce 7 webs in 7 days.
• All spiders work at the same constant rate.
• Find the time for 1 spider to make 1 web.

Concept / Approach:
Let r be web/spider/day. Total webs = (number of spiders) * (days) * r. Solve for r from the given data, then compute the time for a single spider to make one web as 1/r days.

Step-by-Step Solution:

Verification / Alternative check:
Proportionality check: If one spider makes 1 web in 7 days, then 7 spiders make 7 webs in the same 7 days, matching the premise.

Why Other Options Are Wrong:
3, 4, 6, 10 contradict the constant-rate calculation of r = 1/7 web/day per spider.

Common Pitfalls:
Assuming 1 day by incorrectly cancelling numbers, or thinking 7 spiders * 7 days = 49 webs (confusing rate extraction).

Final Answer:
7