Difference between revisions of "1982 AHSME Problems/Problem 6"

m (Add title)
(Solution)
 
Line 7: Line 7:
 
== Solution ==
 
== Solution ==
  
Note that the sum of the interior angles of a convex polygon of <math>n</math> sides is <math>180(n-2)^\circ</math>, and each interior angle belongs to <math>[0, 180^\circ)</math>. Therefore, we must have <math>n - 2 = \lfloor \frac{2570^\circ}{180^\circ} \rfloor = 15</math>. Then the missing angle must be <math>180*15^\circ - 2570^\circ = 130^\circ</math>, so our answer is <math>\boxed{\text{(D)}}</math> and we are done.
+
Note that the sum of the interior angles of a convex polygon of <math>n</math> sides is <math>(n-2) \cdot 180^\circ</math>, and each interior angle is less than <math>180^\circ</math>. Therefore, <math>n - 2 = \left\lfloor \frac{2570^\circ}{180^\circ} \right\rfloor = 15</math>, and the missing angle is <math>15 \cdot 180^\circ - 2570^\circ = 130^\circ \boxed{\text{(D)}}</math> .
  
 
== See also ==
 
== See also ==

Latest revision as of 22:15, 29 June 2025

Problem

The sum of all but one of the interior angles of a convex polygon equals $2570^\circ$. The remaining angle is

$\text{(A)} \ 90^\circ \qquad  \text{(B)} \ 105^\circ \qquad  \text{(C)} \ 120^\circ \qquad  \text{(D)}\ 130^\circ\qquad \text{(E)}\ 144^\circ$

Solution

Note that the sum of the interior angles of a convex polygon of $n$ sides is $(n-2) \cdot 180^\circ$, and each interior angle is less than $180^\circ$. Therefore, $n - 2 = \left\lfloor \frac{2570^\circ}{180^\circ} \right\rfloor = 15$, and the missing angle is $15 \cdot 180^\circ - 2570^\circ = 130^\circ \boxed{\text{(D)}}$ .

See also

1982 AHSME (ProblemsAnswer KeyResources)
Preceded by
Problem 5
Followed by
Problem 7
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
All AHSME Problems and Solutions

These problems are copyrighted © by the Mathematical Association of America, as part of the American Mathematics Competitions. AMC Logo.png