RBI Assistant Formula Sheet
Ten formulas, what each one is for, and a worked example.
RBI Assistant Numerical Ability is close to the bank clerk pattern: simplification, approximation, number series and short arithmetic problems in Prelims, with more word problems and DI in Mains.
These ten formulas cover the arithmetic, with a worked train example.
The 10 Formulas
1
Formula
Percentage change
Expression
(New − Old) ÷ Old × 100
Use it for
Growth and fall in values, and the base of most DI questions.
2
Formula
Profit %
Expression
(SP − CP) ÷ CP × 100
Use it for
Profit or loss on cost price.
3
Formula
Discount and marked price
Expression
SP = MP × (1 − Discount/100)
Use it for
Selling price after a discount on the marked price.
4
Formula
Simple interest
Expression
SI = P × R × T ÷ 100
Use it for
Interest that isn't added back to the principal.
5
Formula
Compound interest
Expression
A = P × (1 + R/100)ᵀ; CI = A − P
Use it for
Interest compounded once a year.
6
Formula
Time and work (two people)
Expression
Days together = (a × b) ÷ (a + b)
Use it for
When A alone takes a days and B alone takes b days.
7
Formula
Speed, distance, time
Expression
Distance = Speed × Time; km/h × 5/18 = m/s
Use it for
Trains, journeys and unit conversions.
8
Formula
Train crossing a platform
Expression
Time = (Train length + Platform length) ÷ Speed
Use it for
A train crossing a pole uses its own length only.
9
Formula
Average
Expression
Sum of observations ÷ Number of observations
Use it for
Averages, and finding a missing or replaced value.
10
Formula
Partnership
Expression
Profit share ∝ Capital × Time
Use it for
Splitting profit between partners who invested for different periods.
| # | Formula | Expression | Use it for |
|---|---|---|---|
| 1 | Percentage change | (New − Old) ÷ Old × 100 | Growth and fall in values, and the base of most DI questions. |
| 2 | Profit % | (SP − CP) ÷ CP × 100 | Profit or loss on cost price. |
| 3 | Discount and marked price | SP = MP × (1 − Discount/100) | Selling price after a discount on the marked price. |
| 4 | Simple interest | SI = P × R × T ÷ 100 | Interest that isn't added back to the principal. |
| 5 | Compound interest | A = P × (1 + R/100)ᵀ; CI = A − P | Interest compounded once a year. |
| 6 | Time and work (two people) | Days together = (a × b) ÷ (a + b) | When A alone takes a days and B alone takes b days. |
| 7 | Speed, distance, time | Distance = Speed × Time; km/h × 5/18 = m/s | Trains, journeys and unit conversions. |
| 8 | Train crossing a platform | Time = (Train length + Platform length) ÷ Speed | A train crossing a pole uses its own length only. |
| 9 | Average | Sum of observations ÷ Number of observations | Averages, and finding a missing or replaced value. |
| 10 | Partnership | Profit share ∝ Capital × Time | Splitting profit between partners who invested for different periods. |
Worked Example: Train Crossing a Pole
A 300 m train runs at 54 km/h. How long does it take to cross a pole?
- 1
Convert speed
54 × 5/18 = 15 m/s.
- 2
Distance covered
Only the train's length, 300 m, because a pole has no length.
- 3
Time
300 ÷ 15 = 20 seconds.
Data interpretation, arithmetic and number series. No signup needed.
Convert Units Before Anything Else
Train and speed questions mix km/h with metres and seconds. Convert km/h to m/s (× 5/18) first and most of the question is done.
FAQs
Is RBI Assistant maths harder than bank clerk exams?expand_more
It's broadly similar. Mains has a separate Numerical Ability paper with more DI.
How many maths questions are in Prelims?expand_more
35 Numerical Ability questions.
What's the difference between crossing a pole and a platform?expand_more
For a platform, add the platform's length to the train's length.
Next steps
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