Fifteen verified shortcuts for high-frequency Quant topics — successive discounts, compound interest, time-work, mixture, and more.
In a 15-minute, 25-question Quant section, every second counts. These shortcuts shave 30–60 seconds off common problem types.
Two discounts a% and b% → net single discount = a + b − (ab/100). Example: 20% + 10% = 30 − 2 = 28%, not 30%.
CI on P at r% for 2 years = P × r × (r + 200) / 10000 Skip the year-by-year calculation.
CI − SI = P × (r/100)². Instant — no formula chain.
If A is k times as efficient as B, A's time = B's time / k. Combined rate = (1 + k) / B's time.
Fill rate = 1/a, empty rate = 1/b. Net rate = (1/a) − (1/b). Time = 1/net rate.
Concentration c1 and c2 mixed → ratio = (c2 − m) : (m − c1), where m = target concentration.
A value x changed by +a% then −b% → net = a − b − (ab/100). Example: +20% then −10% = 20 − 10 − 2 = +8%.
One at x% profit, other at x% loss → always net loss of (x²/100)%.
Old average × n + change = new average × n → change = (new avg − old avg) × n.
Two trains in opposite directions: relative speed = sum. Same direction: difference.
Downstream = boat + stream; upstream = boat − stream. Boat speed = (D + U)/2; stream = (D − U)/2.
LCM × HCF = product of the two numbers. Use this when one is unknown.
Sum: floor(n/5) + floor(n/25) + floor(n/125) + ...
Cyclicity: 2/3/7/8 repeat every 4; 4/9 every 2; 0/1/5/6 every 1.
(n + 1) / 2. For first n even numbers: n + 1.
Memorise these ONCE, then practise them in SSCIntel's Quant topic-wise practice until they're reflex.
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