In this guide
RRB Group D has 25 maths questions out of 100. They are at Class 10 level or below. Very few marks are lost because the questions are too advanced. Most are lost because a candidate is slow, makes a calculation slip, or answers a slightly different question from the one asked.
So this plan is about two things: learning a small set of methods properly, and building speed until each question takes about a minute.
How much time maths gets in the exam
You have 90 minutes for 100 questions, about 54 seconds each. A sensible budget for maths is 25–30 minutes, because some questions need a few lines of working. That means about one minute per maths question. If maths is eating 40 minutes in your mocks, the time is coming out of reasoning and science.
Topic priorities
| Priority | Topics | Why |
|---|---|---|
| High | BODMAS, percentage, ratio, averages, profit and loss, simple and compound interest, time and work, speed and distance | Core arithmetic; each links to the others |
| Medium | Number system, LCM–HCF, decimals and fractions, ages, squares and roots, mensuration | Short rule-based questions; quick marks once learnt |
| Lower | Algebra, geometry, trigonometry, statistics, calendar and clock | Class 10 basics are enough; learn formulas, not long proofs |
"Lower" does not mean "skip". It means these come after the core arithmetic is solid.
A six-week order
| Week | Topics |
|---|---|
| 1 | Tables and squares, number system, BODMAS, decimals and fractions |
| 2 | Percentage, ratio, averages |
| 3 | Profit and loss, simple and compound interest |
| 4 | Time and work, pipes and cisterns, speed and distance, trains |
| 5 | Ages, LCM–HCF, squares and roots, mensuration |
| 6 | Algebra, geometry, trigonometry, statistics, calendar and clock; mixed practice |
Percentage comes early because profit and loss, interest and data questions are all built on it.
A daily routine (60 minutes)
- 10 minutes: mental maths. Tables, squares, percentages, without paper.
- 30 minutes: one topic. Learn the method, then solve 15 questions.
- 15 minutes: 10 mixed questions from past papers, with a timer.
- 5 minutes: write every mistake in an error notebook, with the correct method.
Read the error notebook every Sunday. The same three or four mistakes usually repeat, and seeing them written down is what stops them.
Learn by heart
- Tables up to 20.
- Squares up to 30 and cubes up to 15.
- Speed: km/h × 5/18 = m/s, and m/s × 18/5 = km/h.
- Fractions as percentages:
| Fraction | % | Fraction | % |
|---|---|---|---|
| 1/2 | 50 | 1/8 | 12.5 |
| 1/3 | 33⅓ | 1/9 | 11 1/9 |
| 1/4 | 25 | 1/10 | 10 |
| 1/5 | 20 | 1/12 | 8⅓ |
| 1/6 | 16⅔ | 1/16 | 6.25 |
| 1/7 | 14 2/7 | 1/20 | 5 |
Once you know that 37.5% is 3/8, a question like "37.5% of 480" becomes 480 ÷ 8 × 3 in your head.
Worked examples
Example 1 (profit): A shopkeeper buys an item for ₹200 and sells it for ₹250. What is the profit percentage?
- Profit = 250 − 200 = ₹50.
- Profit % = 50 ÷ 200 × 100 = 25%.
- Profit is calculated on the cost price, not the selling price.
Example 2 (percentage as a fraction): Find 37.5% of 480.
- 37.5% = 3/8.
- 480 ÷ 8 = 60; 60 × 3 = 180.
Example 3 (trains): A train 150 m long runs at 54 km/h. How long does it take to pass a pole?
- 54 km/h = 54 × 5/18 = 15 m/s.
- To pass a pole, the train covers its own length: 150 ÷ 15 = 10 seconds.
Example 4 (time and work): A can finish a job in 12 days and B in 18 days. How long will they take together?
- Take the total work as the LCM of 12 and 18 = 36 units.
- A does 36 ÷ 12 = 3 units a day; B does 36 ÷ 18 = 2 units a day.
- Together: 5 units a day, so 36 ÷ 5 = 7⅕ days (7.2 days).
Example 5 (average): The average of 5 numbers is 24. When one number is removed, the average of the rest is 22. Find the number removed.
- Total of 5 numbers = 5 × 24 = 120.
- Total of 4 numbers = 4 × 22 = 88.
- Number removed = 120 − 88 = 32.
Calculation habits
- Write neatly in rough work. Many "wrong method" errors are really copying errors.
- Check units: km/h or m/s? Hours or minutes? Rupees or paise?
- Before choosing an option, ask: "Did I find what the question asked?"
- If two options are close, don't round. Calculate exactly.
Common errors
- Taking a percentage of the wrong number, for example profit on the selling price.
- Adding percentages that apply to different amounts: a 10% rise then a 10% fall is not zero, it is a 1% fall.
- Stopping at the first step, such as finding the cost price when the question asks for the profit.
Practice set
- Find 15% of 300.
- What is 19²?
- Write 1/6 as a percentage.
- Convert 36 km/h into metres per second.
- An article is sold for ₹360 at a loss of 10%. Find the cost price.
- Convert 72 km/h into metres per second.
- Divide ₹64 in the ratio 3 : 5. What is the larger share?
- Find the simple interest on ₹5,000 at 8% a year for 3 years.
Answers:
- 45. 10% is 30 and 5% is 15; 30 + 15 = 45.
- 361. 19 × 19 = 361.
- 16⅔%. 100 ÷ 6 = 16.67.
- 10 m/s. 36 × 5/18 = 10.
- ₹400. Selling at 10% loss means SP = 90% of CP. 360 ÷ 0.9 = 400.
- 20 m/s. 72 × 5/18 = 20.
- ₹40. 3 + 5 = 8 parts; 64 ÷ 8 = 8; larger share = 5 × 8 = 40.
- ₹1,200. 5,000 × 8 × 3 ÷ 100 = 1,200.
What to do next
- Write the fraction–percentage table on a card and read it daily for a week.
- Start week 1 of the six-week order today.
- Start an error notebook and use it after every practice session.
- In week 6, take two full maths sections under time and aim for 25 minutes.
A note on dates and numbers. Exam patterns, vacancies and schedules change from year to year. Always confirm the current details in the latest notification on the Railway Recruitment Boards website .
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