Bunuel
The price of Darjeeling tea (in rupees per kilogram) is \(100 + 0.10n\), on the \(n_{th}\) day of 2007 (n = 1, 2, ..., 100), and then remains constant. On the other hand, the price of Ooty tea (in rupees per kilogram) is \(89 + 0.15n\), on the \(n_{th}\) day of 2007 (n = 1, 2, ..., 365). On which date in 2007 will the prices of these two varieties of tea be equal? (Note: 2007 was not a leap year)
A. May 21
B. May 20
C. April 20
D. April 11
E. April 10
Since each formula tells us the price on Day n, we can set those two formulas equal to each other.
We get: \(100 + 0.10n=89 + 0.15n\)
Subtract \(89\) from both sides of the equation to get: \(11 + 0.10n=0.15n\)
Subtract \(0.10n\) from both sides of the equation: \(11=0.05n\)
Solve: \(n = \frac{11}{0.05} = 220\)
So, it SEEMS that the two prices will be equal on Day 220
HOWEVER, the formula for the price of Darjeeling tea only goes until Day 100, at which point its price remains the same forever afterwards.
On Day 100, the price of Darjeeling tea = \(100 + 0.10(100) = 100 + 10 = 110\)
So, AFTER Day 100, price of Darjeeling tea = 110 rupees
So let's now determine which day the price of Ooty tea is 110 rupees
We can write the equation: \(89 + 0.15n = 110\)
Subtract \(89\) from both sides to get: \(0.15n = 21\)
Solve: \(n = \frac{21}{0.15} = 140\)
So, on Day 140, the two teas will each sell for 140 rupees per kilogram.
Our job now is to determine what day of the year is Day 140
January has 31 days
February has 28 days (in a non leap year)
March has 31 days
April has 30 days
31 + 28 + 31 + 30 = 120 days.
In other words Day 120 is on April 30th
So, 20 days later (on
May 20th) will be Day 140
Answer: B
Cheers,
Brent