S borrowed some amount from R and promised to pay him 8% interest. Then S invested the borrowed amount in a scheme, upon which he earned a profit of 5% after paying R, the principal amount with interest. How much percentage R would have gained, if he would have invested in the scheme directly?
- (a)14%
- (b)13%
- (c)14.4%
- (d)13.4%
Answer
Why
Correct — B. Take the borrowed sum as ₹100 — only percentages are given, so the base is yours to choose.
What S owes R, principal plus 8% interest:
100 + 8 = ₹108
S's own profit is 5% of the ₹100 he put into the scheme:
= ₹5
So the scheme returned 108 + 5 = ₹113 on an investment of ₹100.
R investing directly would keep all of that: a gain of 13% → option (b).
Why the others are wrong
- (a)14% — Fourteen is a decoy round number. The scheme's return is the 8% that leaves S's hands plus the 5% that stays in them, both measured on the same ₹100, and 8 + 5 is 13.
- (c)14.4% — 14.4 has no route through these numbers. It sits beside the 13.4 decoy so that a mis-based calculation still finds something to pick. The scheme pays ₹113 on ₹100.
- (d)13.4% — 13.4 comes from charging S's 5% profit on the ₹108 he repaid: 108 × 1.05 = 113.4. But the profit is on what S invested, the ₹100 he borrowed, so the scheme returns ₹113.
Concept
This is a middleman chain. S borrows at one rate, invests at a higher one, and keeps the difference. The scheme's true return is everything S receives, not merely what he retains.
Return to the scheme = interest handed to R + profit kept by S.
Percentages may be added only when they sit on the same base. Here both the 8% and the 5% are quoted on the amount borrowed, so 8 + 5 = 13 is legitimate. Change either base and the shortcut breaks.
The question does not spell out what the 5% profit is a percentage of. The key reads it as 5% of the borrowed amount, which puts both percentages on the same ₹100 and gives a clean 13%.
Say the base out loud before you add two percentages.
Key facts
- Percentages may be added only when they are taken on the same base.
- The scheme's return equals the interest S paid out plus the profit S kept.
- With no absolute figures given, set the unknown amount to ₹100 and read the answer off directly.
- 8% interest plus a 5% profit on the same ₹100 is a 13% total return.
Study next
Common traps
- Compounding the 5% on ₹108 instead of taking it on ₹100
- Reading the 5% as R's gain rather than S's
- Treating 'after paying R' as meaning the profit is measured on what is left over
SSC likes the borrow-invest-keep-the-difference chain because it looks like interest and is really percentage bookkeeping. Percentage arithmetic runs through this shift: Quant Q.19 puts cost price at 75% of marked price with a 15% discount, and Quant Q.20 raises a salary by 25% and then cuts it by 12%.
Related PYQs
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