Difficulty: Easy
Correct Answer: 154 sq. cm
Explanation:
Introduction / Context:
This is a mixed-formula circle problem: you are given a linear relation between circumference and radius, and asked for area. The trick is to solve for the radius using the circumference formula and then compute the area using r. Taking π = 22/7 simplifies arithmetic neatly.
Given Data / Assumptions:
Concept / Approach:
From C − r = 37, substitute C = 2πr to get r(2π − 1) = 37. Evaluate 2π − 1 with π = 22/7; solve for r; then compute area A = πr^2.
Step-by-Step Solution:
2π − 1 = 2*(22/7) − 1 = 44/7 − 1 = 37/7r(37/7) = 37 ⇒ r = 37 * (7/37) = 7 cmArea A = πr^2 = (22/7) * 7^2 = (22/7) * 49 = 154 sq. cm
Verification / Alternative check:
Compute C = 2πr = 2*(22/7)*7 = 44 cm. Then C − r = 44 − 7 = 37 cm, matching the condition, confirming r = 7 cm is correct.
Why Other Options Are Wrong:
148 and 111 sq. cm do not correspond to any integer radius under π = 22/7 that satisfies C − r = 37. 259 sq. cm is too large; it would require a radius > 8 cm, contradicting the relation.
Common Pitfalls:
Forgetting to subtract r from C, or using decimal π which complicates the arithmetic here. Using π = 22/7 makes the relation 2π − 1 an exact 37/7, giving r = 7 immediately.
Final Answer:
154 sq. cm
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