When one-seventh of a number is subtracted from the number itself, the result equals the sum of interior angles of a triangle (180 degrees). What is the number?

Introduction / Context:
This algebra problem connects fractions of a number with a known constant from geometry: the sum of angles of a triangle is 180 degrees. It checks the ability to translate words into an equation and solve for the unknown efficiently.

Given Data / Assumptions:

• Let the unknown number be x.
• One-seventh of x is x / 7.
• Sum of angles of any triangle = 180.

Concept / Approach:
Translate the sentence directly: x - (x / 7) = 180. Combine like terms and solve for x using simple fraction arithmetic.

Step-by-Step Solution:

Verification / Alternative check:
Check: 1/7 of 210 is 30; 210 - 30 = 180, which matches the triangle angle sum.

Why Other Options Are Wrong:
224, 140, 350, and 126 do not satisfy x - x/7 = 180 when substituted.

Common Pitfalls:
Subtracting 1/7 incorrectly (e.g., using 1/6 by mistake) or mixing degrees and radians—but only the value 180 matters here.

Final Answer:
210