Interview Q&A / Aptitude

1. How do you calculate successive percentage changes?

   Two changes of a% and b% give a net change of a + b + (a x b) / 100 percent. Use negative values for decreases. For example, a 20% increase followed by a 20% decrease is a net 4% decrease, not zero.

   BeginnerIn-depth3 min read
2. How do you solve profit and loss questions with marked price and discount?

   Profit or loss percent is always calculated on the cost price. Discount percent is always calculated on the marked price. Chain them with multipliers. For example, mark up 25% and give 10% off, and the selling price is 1.25 x 0.9 = 1.125 times the cost, which is a 12.5% profit.

   BeginnerIn-depth4 min read
3. How do you solve ratio and age problems?

   Write the present ages as multiples of one unknown using the given ratio, such as 4x and 5x, then add or subtract the same number of years to both and set up an equation from the second condition. Both people age by the same amount, so the difference between their ages never changes.

   BeginnerIn-depth4 min read
4. How do you solve time and work problems quickly?

   Convert each person's time into work per day (1 divided by days), add rates when people work together, and divide total work by the combined rate. The LCM method makes it faster. Take total work as the LCM of the days, so each rate becomes a whole number.

   BeginnerIn-depth3 min read
5. What is the difference between simple interest and compound interest?

   Simple interest is calculated only on the original principal, so it is the same every year (SI = P x R x T / 100). Compound interest is calculated on the principal plus the interest already earned, so it grows every year (A = P x (1 + R/100)^T). For 2 years, the difference is P x (R/100)^2.

   BeginnerIn-depth4 min read