Problem: An article costing C dollars is sold for $100 at a loss of x percent of the selling price. It is then resold at a profit of x percent of the new selling price S′. If the difference between S′ and C is 191 dollars, then x is:
Answer Choices:
A. undetermined
B. 980
C. 10
D. 995
E. 9100
Solution:
100=C−x,C=100+x
∴S′=C+191=100+x+910=100+100x(100+x+910)
∴100x2+90x−910=0∴x=10