Simple Interest is one of those chapters where the marks are sitting there waiting for you. There is one main formula, and almost every question in bank exams, SSC and railway papers is built on it. The trouble students face is not the formula, it is the reading. Rate is per year, so if the time is given in months, convert it before you touch the calculation. If a question says the sum doubles or triples, do not start plugging in numbers randomly, use the shortcut below and you will finish in ten seconds. Work through these 50 questions with the steps written out, and this chapter will stop costing you time in the exam hall.
Simple Interest Formulas
The main formula
SI = (P × R × T) ÷ 100
Where P = Principal (the sum invested or borrowed), R = Rate of interest per annum, T = Time in years, SI = Simple Interest.
Finding the Amount
A = P + SI
A = P (1 + (R × T) ÷ 100)
Rearranging for the missing value
P = (100 × SI) ÷ (R × T)
R = (100 × SI) ÷ (P × T)
T = (100 × SI) ÷ (P × R)
When the sum becomes n times itself
R × T = (n − 1) × 100
So a sum doubles when R × T = 100, and triples when R × T = 200. This one shortcut clears a large chunk of exam questions.
Converting time correctly
Months to years: T = number of months ÷ 12
Days to years: T = number of days ÷ 365 (count the starting day out, the last day in)
When two different amounts are given for two time periods
SI for one year = (A₂ − A₁) ÷ (T₂ − T₁)
P = A₁ − (SI for one year × T₁)
When a sum is split at different rates
Total SI = (P₁ × R₁ × T₁) ÷ 100 + (P₂ × R₂ × T₂) ÷ 100
60 Simple Interest Aptitude Questions and Answers (Solved MCQs)
Question 1. Find the simple interest on ₹8,000 at 5% per annum for 4 years.
a) ₹1,400
b) ₹1,600
c) ₹1,800
d) ₹2,000
Answer:
b) ₹1,600 — SI = (8000 × 5 × 4)/100 = ₹1,600.
Question 2. A sum of ₹5,000 earns ₹1,500 as simple interest in 6 years. Find the rate.
a) 4%
b) 5%
c) 6%
d) 7%
Answer:
b) 5% — R = (1500 × 100)/(5000 × 6) = 5%.
Question 3. At what rate will ₹12,000 earn ₹2,400 in 5 years?
a) 3%
b) 4%
c) 5%
d) 6%
Answer:
b) 4% — R = (2400 ×100)/(12000×5)=4%.
Question 4. Find the principal if SI is ₹3,000 at 10% for 3 years.
a) ₹8,000
b) ₹9,000
c) ₹10,000
d) ₹11,000
Answer:
c) ₹10,000 — P=(3000×100)/(10×3)=₹10,000.
Question 5. A sum becomes ₹9,200 in 3 years at 5% SI. Find the principal.
a) ₹8,000
b) ₹8,500
c) ₹9,000
d) ₹7,500
Answer:
a) ₹8,000
Question 6. What is the SI on ₹15,000 at 12% for 2 years?
a) ₹3,000
b) ₹3,600
c) ₹4,000
d) ₹4,500
Answer:
b) ₹3,600 — SI=(15000×12×2)/100.
Question 7. A principal earns ₹720 at 6% in 4 years. Find the principal.
a) ₹2,500
b) ₹3,000
c) ₹3,500
d) ₹4,000
Answer:
b) ₹3,000 — P=(720×100)/(6×4).
Question 8. Find the amount on ₹20,000 at 7% SI for 5 years.
a) ₹25,000
b) ₹26,000
c) ₹27,000
d) ₹28,000
Answer:
c) ₹27,000 — SI=₹7,000; Amount=₹27,000.
Question 9. SI on ₹6,000 for 18 months at 10% is:
a) ₹800
b) ₹850
c) ₹900
d) ₹950
Answer:
c) ₹900 — Time=1.5 years. SI=(6000×10×1.5)/100.
Question 10. A sum doubles in 20 years at SI. Find the rate.
a) 4%
b) 5%
c) 6%
d) 7%
Answer:
b) 5% — Interest equals principal in 20 years. Rate=100/20=5%.
Question 11. A sum triples in 16 years at SI. Find the rate.
a) 10%
b) 11.5%
c) 12.5%
d) 15%
Answer:
c) 12.5% — Increase = 200%. Rate=200/16=12.5%.
Question 12. Find SI on ₹9,000 at 8% for 2.5 years.
a) ₹1,600
b) ₹1,700
c) ₹1,800
d) ₹1,900
Answer:
c) ₹1,800 — SI=(9000×8×2.5)/100.
Question 13. A sum becomes ₹13,000 after earning ₹3,000 SI. Find the principal.
a) ₹9,000
b) ₹10,000
c) ₹11,000
d) ₹12,000
Answer:
b) ₹10,000 — Principal = Amount − Interest.
Question 14. Find the rate if ₹10,000 earns ₹4,000 in 8 years.
a) 4%
b) 5%
c) 6%
d) 7%
Answer:
b) 5% — R=(4000×100)/(10000×8).
Question 15. SI on ₹25,000 at 4% for 3 years is:
a) ₹2,500
b) ₹3,000
c) ₹3,500
d) ₹4,000
Answer:
b) ₹3,000 — SI=(25000×4×3)/100.
Question 16. A sum earns ₹2,100 in 7 years at 5%. Find the principal.
a) ₹5,000
b) ₹6,000
c) ₹7,000
d) ₹8,000
Answer:
b) ₹6,000 — P=(2100×100)/(7×5).
Question 17. Find the time if ₹12,000 earns ₹3,600 at 10%.
a) 2 years
b) 3 years
c) 4 years
d) 5 years
Answer:
b) 3 years — T=(3600×100)/(12000×10).
Question 18. SI on ₹18,000 at 15% for 8 months is:
a) ₹1,600
b) ₹1,800
c) ₹2,000
d) ₹2,200
Answer:
b) ₹1,800 — Time=8/12 year.
Question 19. Amount becomes ₹17,250 after 5 years at 9%. Find principal.
a) ₹12,000
b) ₹13,000
c) ₹14,000
d) ₹15,000
Answer:
a) ₹12,000 — Amount=P(1+45/100)=1.45P.
Question 20. A sum becomes ₹22,400 in 4 years at 10%. Find interest.
a) ₹5,600
b) ₹6,000
c) ₹6,400
d) ₹7,000
Answer:
c) ₹6,400
Question 21. SI on ₹16,000 at 7.5% for 4 years is:
a) ₹4,200
b) ₹4,600
c) ₹4,800
d) ₹5,000
Answer:
c) ₹4,800 — SI=(16000×7.5×4)/100.
Question 22. A sum doubles in 25 years. Find SI rate.
a) 3%
b) 4%
c) 5%
d) 6%
Answer:
b) 4% — Rate=100/25.
Question 23. Interest on ₹40,000 for 9 months at 12% is:
a) ₹3,000
b) ₹3,200
c) ₹3,600
d) ₹4,000
Answer:
c) ₹3,600 — SI=(40000×12×9)/(100×12).
Question 24. Principal is ₹8,000 and amount is ₹10,400. Find SI.
a) ₹2,000
b) ₹2,200
c) ₹2,400
d) ₹2,600
Answer:
c) ₹2,400 — A−P.
Question 25. Find rate if amount is 125% of principal after 5 years.
a) 4%
b) 5%
c) 6%
d) 7%
Answer:
b) 5% — Interest=25% in 5 years.
Question 26. A sum earns ₹960 in 2 years at 8%. Find principal.
a) ₹5,000
b) ₹6,000
c) ₹7,000
d) ₹8,000
Answer:
b) ₹6,000.
Question 27. SI on ₹7,500 at 16% for 15 months is:
a) ₹1,400
b) ₹1,500
c) ₹1,600
d) ₹1,700
Answer:
b) ₹1,500.
Question 28. Find time if amount is 140% of principal at 8%.
a) 4 years
b) 5 years
c) 6 years
d) 7 years
Answer:
b) 5 years — Interest=40%.
Question 29. A principal of ₹30,000 earns ₹10,800. Find rate if time is 6 years.
a) 5%
b) 6%
c) 7%
d) 8%
Answer:
b) 6%.
Question 30. Amount on ₹50,000 at 8% for 2 years is:
a) ₹56,000
b) ₹57,000
c) ₹58,000
d) ₹59,000
Answer:
c) ₹58,000.
Question 31. The SI on a sum for 5 years is half the principal. Find rate.
a) 8%
b) 10%
c) 12%
d) 15%
Answer:
b) 10% — 50% = R×5.
Question 32. A sum becomes ₹18,000 in 5 years and ₹20,400 in 7 years. Find annual interest.
a) ₹1,000
b) ₹1,100
c) ₹1,200
d) ₹1,300
Answer:
c) ₹1,200 — Difference over 2 years = ₹2,400.
Question 33. Find principal from Q32.
a) ₹12,000
b) ₹13,000
c) ₹14,000
d) ₹15,000
Answer:
a) ₹12,000 — 5-year interest = ₹6,000.
Question 34. A sum doubles in 12.5 years. Find rate.
a) 6%
b) 7%
c) 8%
d) 9%
Answer:
c) 8%.
Question 35. Two sums are in ratio 2:3. At same rate and time, interests are in ratio:
a) 2:3
b) 3:2
c) 4:9
d) 1:1
Answer:
a) 2:3.
Question 36. A sum earns ₹4,800 in 8 years at 6%. Find amount.
a) ₹13,800
b) ₹14,000
c) ₹14,800
d) ₹15,000
Answer:
c) ₹14,800.
Question 37. Interest for 3 years is ₹1,350. What is interest for 8 years?
a) ₹3,200
b) ₹3,400
c) ₹3,600
d) ₹3,800
Answer:
c) ₹3,600.
Question 38. A sum earns 24% of itself in 6 years. Find rate.
a) 3%
b) 4%
c) 5%
d) 6%
Answer:
b) 4%.
Question 39. ₹5,000 invested at 8% and ₹8,000 at 10%. Total annual SI?
a) ₹1,000
b) ₹1,100
c) ₹1,200
d) ₹1,300
Answer:
c) ₹1,200.
Question 40. A sum becomes ₹16,800 in 4 years and ₹18,000 in 5 years. Find principal.
a) ₹12,000
b) ₹13,000
c) ₹14,000
d) ₹15,000
Answer:
a) ₹12,000.
Question 41. A sum becomes ₹13,200 in 4 years and ₹14,850 in 7 years. Find principal.
a) ₹9,800
b) ₹10,000
c) ₹11,000
d) ₹12,000
Answer:
c) ₹11,000 — Annual SI=₹550.
Question 42. A sum earns ₹9,000 in 15 years. Find annual interest.
a) ₹500
b) ₹600
c) ₹700
d) ₹800
Answer:
b) ₹600.
Question 43. If SI equals 60% of principal in 12 years, find rate.
a) 4%
b) 5%
c) 6%
d) 7%
Answer:
b) 5%.
Question 44. A sum triples in 20 years. Find rate.
a) 8%
b) 9%
c) 10%
d) 12%
Answer:
c) 10%.
Question 45. A principal of ₹25,000 earns ₹15,000. Find time at 10%.
a) 5 years
b) 6 years
c) 7 years
d) 8 years
Answer:
b) 6 years.
Question 46. A sum becomes ₹24,000 in 5 years and ₹28,000 in 10 years. Find principal.
a) ₹16,000
b) ₹18,000
c) ₹20,000
d) ₹22,000
Answer:
c) ₹20,000.
Question 47. A sum doubles in x years. Another sum triples in same period. Find second rate if first rate is 8%.
a) 12%
b) 14%
c) 16%
d) 18%
Answer:
c) 16% — x=12.5 years.
Question 48. Difference between amounts after 4 and 7 years is ₹2,700. Find annual SI.
a) ₹800
b) ₹900
c) ₹1,000
d) ₹1,100
Answer:
b) ₹900.
Question 49. A sum earns 75% of itself in 15 years. Find rate.
a) 4%
b) 5%
c) 6%
d) 7%
Answer:
b) 5%.
Question 50. Principal and SI are in ratio 5:2 after 8 years. Find rate.
a) 4%
b) 5%
c) 6%
d) 7%
Answer:
b) 5%.
Question 51. Amount is ₹18,750 and interest is ₹3,750. Find principal.
a) ₹12,500
b) ₹15,000
c) ₹16,000
d) ₹17,500
Answer:
b) ₹15,000.
Question 52. A sum doubles in 8 years. Find amount after 5 years if principal is ₹20,000.
a) ₹30,000
b) ₹32,500
c) ₹35,000
d) ₹37,500
Answer:
b) ₹32,500.
Question 53. Interest for 15 years is ₹18,000. What is interest for 10 years?
a) ₹10,000
b) ₹11,000
c) ₹12,000
d) ₹13,000
Answer:
c) ₹12,000.
Question 54. Amount after 8 years is ₹14,400 and principal ₹12,000. Find rate.
a) 2%
b) 2.5%
c) 3%
d) 4%
Answer:
b) 2.5%.
Question 55. A sum earns ₹8,000 in 10 years and ₹12,000 in 15 years. Find annual interest.
a) ₹700
b) ₹800
c) ₹900
d) ₹1,000
Answer:
b) ₹800.
Question 56. If amount is 160% of principal after 12 years, find rate.
a) 4%
b) 5%
c) 6%
d) 7%
Answer:
b) 5%.
Question 57. A sum becomes ₹9,000 in 2 years and ₹10,500 in 5 years. Find principal.
a) ₹8,000
b) ₹7,500
c) ₹7,000
d) ₹6,500
Answer:
c) ₹7,000.
Question 58. A sum becomes 1.8 times in 16 years. Find rate.
a) 4%
b) 5%
c) 6%
d) 7%
Answer:
b) 5%.
Question 59. SI is ₹4,500 and principal is ₹15,000. Find percentage gain over principal.
a) 25%
b) 30%
c) 35%
d) 40%
Answer:
b) 30%.
Question 60. A sum becomes ₹30,000 in 8 years and ₹35,000 in 13 years. Find principal.
a) ₹22,000
b) ₹20,000
c) ₹18,000
d) ₹25,000
Answer:
a) ₹22,000 — Annual interest = ₹1,000. Interest for 8 years = ₹8,000. Principal = ₹30,000 − ₹8,000 = ₹22,000.
