Most students who fail placement aptitude tests know the concepts. They run out of time. The fix is to recognise the question type and use the shortest reliable method. Here are ten shortcuts we teach in our aptitude training, each with an example.
1. Successive percentage change
For two changes of a% and b%, the net change is a + b + ab/100. Use a minus sign for a decrease.
Example: a price rises 20% then falls 10%: 20 − 10 − 2 = 8% increase.
2. Same selling price, x% gain and x% loss
There is always a net loss of x²/100 %. With 10% gain on one item and 10% loss on another, the overall loss is 1%.
3. The swap trick
x% of y = y% of x. 16% of 25 is hard; 25% of 16 is 4.
4. A new item changes the average
If the average of n items is A and adding one item raises it by d, the new item is A + (n + 1)d.
Example: 10 students average 40; a new student raises the average by 2, so the new student scored 40 + 11 × 2 = 62.
5. Two people working together
If A takes a days and B takes b days, together they take ab/(a + b) days. 10 and 15 days give 150/25 = 6 days.
6. The LCM method for work problems
Assume the total work equals the LCM of the days and work in units per day. For 12 and 18 days, total work is 36 units, and the rates are 3 and 2 units per day, so together they take 36/5 = 7.2 days. This method also handles three or more people easily.
7. Average speed is not the simple average
For equal distances at x and y, average speed is 2xy/(x + y). Going at 40 km/h and returning at 60 km/h gives 48 km/h, not 50.
8. Trains in one table
- Crossing a pole: length ÷ speed
- Crossing a platform: (train + platform) ÷ speed
- Two trains, opposite directions: (L1 + L2) ÷ (s1 + s2)
- Two trains, same direction: (L1 + L2) ÷ (s1 − s2)
Convert km/h to m/s by multiplying by 5/18.
9. Compound minus simple interest
For 2 years, CI − SI = P(R/100)². On ₹10,000 at 10%, the difference is ₹100.
10. Squares of numbers ending in 5
Multiply the front part by the next number and write 25: 65² → 6 × 7 = 42 → 4225.
How to use these in the test
Make two passes. In the first, answer only the questions you can solve in under 40 seconds. In the second, return to the rest. Never spend more than 90 seconds on one question, and eliminate options before calculating.
Questions
How long does it take to get fast at aptitude?
With 45 minutes of focused practice a day, most students see a big improvement in speed within 3 to 4 weeks.
Are Vedic maths tricks allowed in placement tests?
Yes. They are just faster ways to calculate, and they help most in the quantitative section.