Quantitative aptitude interview questions

I first identify what is given and what is asked, and write the base value or rate. Then I estimate a rough answer before calculating, so I can catch a mistake. If the method is not clear, I try small numbers, like assuming the cost is 100, to see the pattern.

No. Starting at 100, a 20% rise gives 120, and 20% of 120 is 24, so it falls to 96. The net change is a 4% decrease, because the second percentage is taken from a larger base.

Simple interest is calculated only on the original principal, so it is the same every year. Compound interest is calculated on the principal plus interest already added, so it grows each year. For example, 10,000 at 10% for 2 years gives 2,000 simple interest but 2,100 compound interest.

A does 1/10 per day and B does 1/15 per day. Using 30 as the common denominator, that is 3/30 + 2/30 = 5/30 = 1/6 per day. So together they need 6 days, which makes sense because it is less than A's 10 days.

I break them into easy parts. 10% is dividing by 10 and 5% is half of that, so 15% of 640 is 64 + 32 = 96. I also remember common fractions, such as 25% being a quarter and 12.5% being an eighth.

Because average speed is total distance divided by total time, and you spend more time at the slower speed. Going 60 km at 30 km/h and back at 60 km/h takes 3 hours for 120 km, so the average is 40 km/h, not 45.