Bunuel
On Monday, Elena had a certain amount of money in her savings account. On Tuesday, she increased that amount by
m percent. On Wednesday, she withdrew
n percent of her Tuesday balance, leaving her with exactly 50 percent of what she had on Monday. What is the value of
n in terms of
m?
A. \(\frac{100(m + 50)}{m + 100}\)
B. \( \frac{100(m - 50)}{m + 100}\)
C. \( \frac{100(m + 50)}{100 - m}\)
D. \( \frac{100m}{m + 100}\)
E. \( \frac{100(50 - m)}{m - 100}\)
GMAT Club Official Explanation:
Assuming she had $x on Monday, then:
On Tuesday, she’d have \(x(1 + \frac{m}{100})\)
On Wednesday, she’d have \(x(1 + \frac{m}{100}) (1 - \frac{n}{100})\)
Since that amount was 50 percent of what she had on Monday, then:
\(x(1 + \frac{m}{100}) (1 - \frac{n}{100}) =\frac{x}{2}\)
\((1 + \frac{m}{100}) (1 - \frac{n}{100}) =\frac{1}{2}\)
\((\frac{100 + m}{100}) (1 - \frac{n}{100}) =\frac{1}{2}\)
\((1 - \frac{n}{100}) =\frac{50}{100 + m }\)
\(\frac{100 - n}{100} =\frac{50}{100 + m }\)
\(100 - n =\frac{5,000}{100 + m }\)
\(n = 100 - \frac{5,000}{100 + m }\)
\(n = \frac{10,000 + 100m - 5,000}{100 + m }\)
\(n = \frac{5,000 + 100m}{100 + m }\)
\(n = \frac{100(50 + m)}{100 + m }\)
Answer: A.