Interview puzzles and aptitude
Puzzles
3 switches outside, 3 bulbs inside; one entry. Which switch is which bulb?
Turn on switch 1 for a few minutes, turn it off, turn on switch 2, then enter. The lit bulb is 2, the warm off bulb is 1 and the cold off bulb is 3.
25 horses, 5 tracks, no timer. Minimum races to find the top 3?
7. Run 5 heats, race the 5 winners, then one final race with the remaining candidates.
Two ropes, each burns unevenly in 60 min. Measure 45 min?
Light rope A at both ends and rope B at one end. When A finishes (30 min), light B's other end. B finishes 15 min later, at 45 min.
8 balls, one heavier; balance scale. Minimum weighings?
2. Weigh 3 vs 3. If balanced, weigh the remaining 2. If not, take the heavier 3 and weigh 1 vs 1.
A bat and ball cost $1.10; the bat costs $1 more than the ball. Ball price?
$0.05, not $0.10.
Clock angle at 3:15?
7.5°. The hour hand moves 0.5°/min: 90 + 7.5 − 90 = 7.5°.
100 doors, 100 people toggling multiples. Which doors stay open?
Perfect squares (1, 4, 9, … 100): 10 doors, because they have an odd number of divisors.
4 L and 9 L jugs; measure 6 L.
Fill 9, pour into 4 (5 left), empty 4, pour into 4 (1 left), empty 4, pour the 1 in, fill 9, pour into 4 (3 added → 9 − 3 = 6).
How many times do clock hands overlap in 24 h?
22, not 24.
Estimate: how many piano tuners in Mumbai? (Fermi problem)
Break it down: population → households → share owning pianos → tunings per year → tunings per tuner. Show your reasoning; the exact number doesn't matter.
Aptitude topics
- Quantitative: Percentages, ratios, time and work, time–speed–distance, profit and loss, probability, permutations and combinations.
- Logical: Series, coding–decoding, blood relations, seating arrangements, syllogisms, data sufficiency.
- Verbal: Reading comprehension, sentence correction, para-jumbles.