Puzzles : Challenging Mathematical Puzzles
85. In the middle of the confounded desert, there is the
lost city of "Ash". To reach it, I will have to travel overland by
foot from the coast. On a trek like this, each person can only carry enough
rations for five days and the farthest we can travel in one day is 30 miles.
Also, the city is 120 miles from the starting point.
What I am trying to figure out is the fewest number of persons, including
myself, that I will need in our Group so that I can reach the city, stay
overnight, and then return to the coast without running out of supplies.
How many persons (including myself) will I need to accomplish this mission?
Answer : -
Total 4 persons (including you) required.
It is given that each person can only carry enough rations for five days. And
there are 4 persons. Hence, total of 20 days rations is available.
1. First Day : 4 days of rations are used up. One person goes back using one day
of rations for the return trip. The rations remaining for the further trek is
for 15 days.
2. Second Day : The remaining three people use up 3 days of rations. One person
goes back using 2 days of rations for the return trip. The rations remaining for
the further trek is for 10 days.
3. Third Day : The remaining two people use up 2 days of rations. One person
goes back using 3 days of rations for the return trip. The rations remaining for
the further trek is for 5 days.
4. Fourth Day : The remaining person uses up one day of rations. He stays
overnight. The next day he returns to the coast using 4 days of rations.
Thus, total 4 persons, including you are required.
86. At what time after 4.00 p.m. is the minutes hand of
a clock exactly aligned with the hour hand?
Answer : - 4:21:49.5
Assume that X minutes after 4.00 PM minute hand exactly aligns with and hour
For every minute, minute hand travels 6 degrees.
Hence, for X minutes it will travel 6 * X degrees.
For every minute, hour hand travels 1/2 degrees.
Hence, for X minutes it will travel X/2 degrees.
At 4.00 PM, the angle between minute hand and hour hand is 120 degrees. Also,
after X minutes, minute hand and hour hand are exactly aligned. So the angle
with respect to 12 i.e. Vertical Plane will be same. Therefore,
6 * X = 120 + X/2
12 * X = 240 + X
11 * X = 240
X = 21.8182
X = 21 minutes 49.5 seconds
Hence, at 4:21:49.5 minute hand is exactly aligned with the hour hand.
87. Substitute digits for the letters to make the
following Division true
O U T
S T E M | D E M I S E
| D M O C
T U I S
S T E M
Z Z Z E
Z U M M
I S T
Note that the leftmost letter can't be zero in any word. Also, there must be a
one-to-one mapping between digits and letters. e.g. if you substitute 3 for the
letter M, no other letter can be 3 and all other M in the puzzle must be 3.
C=0, U=1, S=2, T=3, O=4, M=5, I=6, Z=7, E=8, D=9
It is obvious that U=1 (as U*STEM=STEM) and C=0 (as I-C=I).
S*O is a single digit and also S*T is a single digit. Hence, their values (O, S,
T) must be 2, 3 or 4 (as they can not be 0 or 1 or greater than 4).
Consider, STEM*O=DMOC, where C=0. It means that M must be 5. Now, its simple.
O=4, S=2, T=3, E=8, Z=7, I=6 and D=9.
O U T 4 1 3
S T E M | D E M I S E 2 3 8 5 | 9 8 5 6 2 8
| D M O C | 9 5 4 0
T U I S 3 1 6 2
S T E M 2 3 8 5
Z Z Z E 7 7 7 8
Z U M M 7 1 5 5
I S T 6 2 3
Also, when arranged from 0 to 9, it spells CUSTOMIZED.
88. In the town called Alibaug, the following facts are
* No two inhabitants have exactly the same number of hairs.
* No inhabitants has exactly 2025 hairs.
* There are more inhabitants than there are hairs on the head of any one
What is the largest possible number of the inhabitants of Alibaug?
Answer : - 2025
It is given that no inhabitants have exactly 2025 hairs. Hence there are 2025
inhabitants with 0 to 2024 hairs in the head.
Suppose there are more than 2025 inhabitants. But these will violate the
condition that "There are more inhabitants than there are hairs on the head
of any one inhabitants." As for any number more than 2025, there will be
same number of inhabitants as the maximum number of hairs on the head of any