Numerical Ability · Editorial

Basic operations (Numerical)

Basic operations reviewer for the CSE Numerical Ability test: fractions, decimals, percent, ratio, and order of operations without a calculator, with practice items.

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CSEPass editorial teamUpdated Facts checked How we source facts5 min readEditorial

Basic-operations items cover the arithmetic you must do quickly without a calculator: fractions, decimals, percent, ratios, and order of operations. On CSE-PPT Numerical Ability, small slips (decimal place, percent vs. percentage points) cost easy points.

Key takeaways

  • Calculators are not allowed on the CSE-PPT, so fast, careful arithmetic by hand is the whole skill.
  • Follow MDAS: multiplication and division (left to right) before addition and subtraction; parentheses first.
  • Memorize common fraction–decimal–percent equivalents; they turn long division into one step.
  • Estimate before computing to eliminate impossible choices.

Fraction, decimal, and percent equivalents

FractionDecimalPercent
1/20.550%
1/30.333…33⅓%
1/40.2525%
1/50.220%
1/80.12512.5%
3/40.7575%
2/50.440%
3/80.37537.5%

Shortcuts that save time

  • 10% of a number: move the decimal one place left (10% of 2,450 = 245). Build 5%, 15%, 20% from it.
  • Multiply by 25: multiply by 100, then divide by 4 (36 × 25 = 3,600 ÷ 4 = 900).
  • Divide by 5: multiply by 2, then divide by 10 (340 ÷ 5 = 680 ÷ 10 = 68).
  • Percent increase: (new − old) ÷ old × 100.
  • Dividing fractions: multiply by the reciprocal (2/3 ÷ 4/9 = 2/3 × 9/4 = 3/2).

How to approach

  1. Rewrite before you compute. Convert mixed numbers, align decimals, or turn percent into fractions (/100).
  2. Estimate first. A rough range kills impossible options (e.g., 18% of ₱2,500 cannot be ₱2,000).
  3. Mind PEMDAS/MDAS. Parentheses and multiplication/division before addition/subtraction.
  4. Keep units and pesos tidy. Label partial answers so you don’t add ₱ to a bare count.
  5. Simplify fractions early. Cancel common factors before multiplying large numbers by hand.

Worked example

Stem: A flash sale takes 20% off a ₱1,450 jacket. How much does Ana pay if she also uses a ₱50 voucher after the discount?

  1. A.₱1,110
  2. B.₱1,160
  3. C.₱1,110.50
  4. D.₱1,400

Work: 20% of 1,450 = 0.20 × 1,450 = 290. Price after discount = 1,450 − 290 = 1,160. Then voucher: 1,160 − 50 = 1,110. Apply percent first, then the flat voucher (unless a stem says otherwise). Answer: A. ₱1,110.

Common traps

  • Percent of vs. percent more — Treating “20% more than 80” as 20% of 80 only.
  • Discount stacking order — Subtracting a voucher before the percent when the stem says after discount.
  • Decimal shift — 0.5 × 36 written as 1.8 instead of 18.
  • Fraction upside-down — Dividing by 2/3 as ×2/3 instead of ×3/2.
  • Calculator fantasy — Leaving an exact fraction half-simplified and mis-copying to the answer sheet.

Quick practice

  1. What is 3/4 of ₱960?
  1. A.₱620
  2. B.₱720
  3. C.₱740
  4. D.₱800

Answer: B — (3×960)/4 = 2,880/4 = 720.

  1. 0.6 + 0.15 × 4 = ?
  1. A.3.0
  2. B.1.2
  3. C.0.75
  4. D.2.4

Answer: B — Multiply first: 0.15×4=0.6; then 0.6+0.6=1.2.

  1. 48 − 6 × 3 + 12 ÷ 4 = ?
  1. A.129
  2. B.33
  3. C.30
  4. D.45

Answer: B — 6 × 3 = 18 and 12 ÷ 4 = 3, so 48 − 18 + 3 = 33.

  1. A price rose from ₱800 to ₱920. What is the percent increase?
  1. A.12%
  2. B.13%
  3. C.15%
  4. D.120%

Answer: C — (920 − 800) ÷ 800 = 120 ÷ 800 = 0.15 = 15%.

  1. 2/3 ÷ 4/9 = ?
  1. A.8/27
  2. B.3/2
  3. C.2/3
  4. D.6/4

Answer: B — 2/3 × 9/4 = 18/12 = 3/2.

  1. What is 37.5% of 640?
  1. A.220
  2. B.240
  3. C.250
  4. D.260

Answer: B — 37.5% = 3/8, and 640 × 3/8 = 240.

Frequently asked questions

Can I use a calculator in the Civil Service Exam?

No. Calculators and other electronic devices are not allowed in the testing room, so practice computing by hand.

What math topics are in Numerical Ability?

CSC lists basic operations, word problems, and number series (sequences). Basic operations covers whole numbers, fractions, decimals, percent, and ratio.

How do I get faster at mental math?

Memorize common fraction–percent equivalents, use shortcuts like 10% and ×25, and estimate before you compute so you can skip choices that cannot be right.

Study with this product

  1. Take the free diagnostic to see if this topic is a weakness.
  2. Drill Basic operations in Practice, or follow Today’s plan for short timed sets.
  3. Sit a full mock when recommended so arithmetic speed holds under whole-exam pressure.

Honest facts

  • This guide is a study aid, not an official CSC reviewer and not a pass promise.
  • We never invent official CSC dates, fees, or room assignments.
  • Sample stems here are original practice items for skill-building, not leaked exam content.
  • Readiness Score is a product metric — not a CSC rating prediction.

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