Civil Service Exam (Subprofessional) Numerical Ability — Basic Statistics & Consecutive NumbersRevision Notes

Formulas

Exam Tips

• Always write down what you're looking for before starting calculations
• Use the sum formula (Sum = Average × Number) as your main tool
• Check if your answer makes logical sense compared to given values
• Practice mental math for common calculations to save time

Key Points

• Average (mean) is the sum of all values divided by the number of values
• Use the sum formula to find missing terms or total values
• Weighted average considers the importance or frequency of each value
• Always identify what the problem is asking for before solving

Definitions

Section Title

Basic Statistical Measures

Common Mistakes

• Forgetting to convert mixed numbers to improper fractions before calculating
• Not identifying whether the problem asks for a missing term or a new average
• Confusing simple average with weighted average when groups have different sizes
• Making arithmetic errors when adding or subtracting large numbers

Formulas

Exam Tips

• Memorize key conversion factors: 12 inches = 1 foot, 3 feet = 1 yard, 7 days = 1 week
• Always set up conversion as a fraction to ensure proper unit cancellation
• Double-check that your final answer has the correct units
• Practice with both exact and approximate conversions

Key Points

• Master common conversion factors used in Philippine exams
• Use dimensional analysis to ensure correct unit conversions
• Pay attention to whether the answer should be a fraction or decimal
• Practice converting between metric and imperial systems

Definitions

Section Title

Unit Conversion

Common Mistakes

• Using incorrect conversion factors (e.g., 1 foot = 10 inches instead of 12)
• Forgetting to cancel units properly in dimensional analysis
• Not converting mixed numbers to improper fractions before multiplying
• Rounding too early in multi-step conversions

Formulas

Exam Tips

• Draw diagrams or use visual representations for complex fraction problems
• Always check if fractions need to add up to 1 (whole)
• Practice finding common denominators quickly
• Verify answers by substituting back into the original problem

Key Points

• Identify what fraction represents the whole in each problem
• Use addition and subtraction to find missing parts
• Convert mixed numbers to improper fractions for easier calculation
• Set up equations when dealing with relationships between parts

Definitions

Section Title

Fraction Word Problems

Common Mistakes

• Adding fractions without finding common denominators
• Forgetting that fractions in word problems often don't add up to 1
• Misinterpreting 'of' as addition instead of multiplication
• Not converting mixed numbers before performing operations

Formulas

Exam Tips

• Always define your variable clearly (what does n represent?)
• Check your answer by substituting back into the original conditions
• Practice recognizing consecutive number patterns in word problems
• Use algebraic methods rather than guess-and-check for efficiency

Key Points

• Consecutive integers differ by 1: n, n+1, n+2, etc.
• Consecutive even numbers differ by 2: n, n+2, n+4, etc.
• Consecutive odd numbers also differ by 2: n, n+2, n+4, etc.
• Use algebraic expressions to represent consecutive numbers

Definitions

Section Title

Consecutive Numbers

Common Mistakes

• Using wrong increments (using +1 for even numbers instead of +2)
• Setting up incorrect equations for word problems
• Forgetting to check if solutions are actually consecutive
• Confusing consecutive integers with consecutive even/odd numbers