Simple Interest Questions for SSC GD

What is Simple Interest?

When you borrow money or deposit money in a bank, the extra money paid or earned on the original amount is called Interest. In Simple Interest, this extra amount is always calculated on the original Principal only — it does not change year after year. Think of it like paying a fixed rent every year on the money you borrowed. The Principal is the original sum, Rate is the percentage charged per year, and Time is how many years.

• Principal (P): The original amount borrowed or deposited.
• Rate (R): Interest charged per year, written as percentage.
• Time (T): Number of years the money is kept or borrowed.
• SI is always calculated on the original Principal, not on accumulated interest.
• Total Amount (A) = Principal + Simple Interest.
• SI grows in a straight line — equal interest every year.

Shortcut — When Rate or Time Doubles

SSC GD often gives a twist: what happens to SI if Rate is doubled or Time is tripled? Since SI = (P x R x T) / 100, all three variables are directly proportional. If you double R, SI doubles. If you triple T, SI triples. This is a very quick one-step answer if you understand proportionality. No need to recalculate from scratch.

• SI is directly proportional to P, R, and T individually.
• Double the Rate — SI doubles (Principal and Time unchanged).
• Halve the Time — SI also halves.
• If both Rate and Time are doubled, SI becomes 4 times.
• These proportion tricks save 30-40 seconds per question.

Finding Rate or Time from Amount

Some SSC GD questions give the final Amount (not SI directly) and ask for Rate or Time. The trick is to first subtract Principal from Amount to get SI, then use the standard formula. Many students panic because Amount is given instead of SI — do not fall for that trap. Just find SI first, then proceed normally.

• Always do: SI = Amount minus Principal as the first step.
• Then use R = (SI x 100) / (P x T) or T = (SI x 100) / (P x R).
• Questions may state money doubles or triples — use that to find SI quickly.
• If money doubles: SI = P (because A = 2P means SI = P).
• If money triples: SI = 2P.

• Using Amount instead of Principal in the SI formula. Always check: is the number given the original sum or the final amount?
• Forgetting to divide by 100 in SI = (P x R x T) / 100. Writing SI = P x R x T gives a wrong answer 100 times larger.
• Confusing Simple Interest with Compound Interest. In SI, interest is always on original Principal. No interest on interest.
• When time is given in months, not converting to years. For example, 6 months = 6/12 = 0.5 years. Use T = 0.5 in formula, not T = 6.
• Missing the last step: question asks for Amount but student writes SI as the final answer. Always add P + SI at the end if Amount is asked.

• Formula hook PRT100: Remember the phrase Pretty Relaxed Tiger — P for Pretty (Principal), R for Relaxed (Rate), T for Tiger (Time), all divided by 100. SI = PRT/100.
• Money doubles trick: Double money means SI equals Principal. Rate = 100 divided by Time. Simple as that.
• Proportionality shortcut: Think of SI as a rectangle area — Length is R, Width is T, Height is P. Increase any side, area grows equally. Double the side, double the area.
• Month to Year trick: Months divided by 12 gives you Time in years. 9 months = 9/12 = 3/4. Write it as fraction directly in formula.

• SSC GD typically asks 1 to 2 questions from this topic. They are usually direct formula application — no complex twists. Do not overthink.
• The most common question type is: SI or Amount is given, find one missing variable (P, R, or T). Practice all three reverse formulas equally.
• Money doubling or tripling questions appear frequently. Memorize: double means R x T = 100, triple means R x T = 200. This gives the answer in under 10 seconds.
• Time is often given in months in some questions — this is a deliberate trap. Always convert months to years before substituting in the formula.
• Target to solve each SI question in under 60 seconds. These are easy scoring questions — do not spend more than 1 minute. If stuck, move on and return.