Last year's sales = $320 million;
This year's sales = $385 million;
Increase = $65 million.

Now, 20% of $320 million is $64 million, which is very close to actual increase of $65 million.

Answer: C.

OR:
General formula for percent increase or decrease, or percent change:

\(Percent=\frac{Change}{Original}*100\) --> \(Percent=\frac{65}{320}*100=\frac{13}{64}*100\approx{\frac{13}{65}}*100=20%\).

Answer: C.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

65 is the closest multiple of 13: 5*13=65.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Increase = 385 - 320 = 65

% Increase \(= \frac{65}{320} * 100 = 20%\)

Answer = C
_________________

Kindly press "+1 Kudos" to appreciate

The problem is testing us on using the percent change formula:

(New Value – Old Value)/Old Value x 100

We are given:

February sales this year = 385 million

February sales last year = 320 million

We need to determine the percent increase between sales from last year to sales this year.

Thus, the new value = 385 million and the old value = 320 million. Let’s plug them into our percent change formula.

(New Value – Old Value)/Old Value x 100

[(385 – 320)/320] x 100

65/320 x 100

13/64 x 100 ≈ 13/65 x 100 ≈ 1/5 x 100 ≈ 20%.

The answer is C.
_________________

Percentage increase = \(\frac{(Final - Original)}{Original}*100\)

\(\frac{(385 - 320)}{320}*100\)

\(\frac{(65)}{320}*100\)

\(\frac{(65)}{32}*10\) Cross off a zero from 320 and 100

\(\frac{65}{32}\) is close to 2, so 2 * 10 = 20%

Answer is C