Interview Q&A / Aptitude

1. 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
2. A sum at simple interest amounts to ₹7,200 in 2 years and ₹8,400 in 4 years. Find the principal and the rate.

   Principal ₹6,000 and rate 10% per year. Two extra years added ₹1,200, so yearly interest is ₹600. Two years of interest is ₹1,200, so P = 7,200 - 1,200 = ₹6,000, and R = 600/6,000 = 10%.

   BeginnerQuick answer1 min read
3. A sum doubles itself in 8 years at simple interest. What is the rate, and in how many years will it become three times?

   The rate is 12.5% per year, because the interest in 8 years equals the principal: 100% / 8 = 12.5%. To triple, the interest must be 200% of the principal, which takes 200 / 12.5 = 16 years.

   BeginnerQuick answer1 min read