Puzzle 1
I recently gave a new watch to my friend for their birthday.
However, as usual with my presents, it was quite useless as it gains 6 minutes every hour.
I set it using my own accurate clock at midnight, and the watch now shows 8:26am.
I know that it stopped 30 minutes ago, so what is the correct time now?
Puzzle Copyright © Kevin Stone
workings
hint
answer
print
Share link: https://www.brainbashers.com/ puzzle/zjxk
Hint
How many watch minutes pass in a real hour?
Answer
8:10am.
Reasoning
The watch now shows 8:26am, so we know that 8 x 60 + 26 = 506 watch minutes have passed.
Since the watch is gaining 6 minutes every hour, for every real hour that has passed, the watch will show 66 minutes.
So, 506 ÷ 66 ≈ 7.666 real hours have passed.
This equals 460 minutes, which is 7 hours and 40 minutes = 7:40am.
The watch stopped 30 minutes ago, therefore the time must now be 8:10am.
Puzzle 2
At the local racetrack, Alex was testing the latest car.
During the eight test laps, Alex managed to average the first two laps at 100mph, the next two laps at 102mph, the next two laps at 140mph, and the last two laps at 150mph.
What was the average speed for the entire 8 laps?
Puzzle Copyright © Kevin Stone
workings
hint
answer
print
Share link: https://www.brainbashers.com/ puzzle/zbip
Hint
Remember that Time = Distance ÷ Speed, and try setting the track length to be a random length.
Answer
119mph.
Reasoning
It doesn't matter how long a lap is, so let's set the track length to be a random number, say 5 miles.
Using:
Time = Distance ÷ Speed
The first two laps took:
10 /100 hours
The second two laps took:
10 /102 hours
The next two laps took:
10 /140 hours
The final two laps took:
10 /150 hours
Therefore, the total time for the 8 laps was:
10 /100 + 10 /102 + 10 /140 + 10 /150 hours
= 1 /10 + 5 /51 + 1 /14 + 1 /15 hours
Looking at the denominators:
10 = 2 x 5
51 = 3 x 17
14 = 2 x 7
15 = 3 x 5
The lowest common multiple (LCM) of these numbers is 2 x 3 x 5 x 7 x 17 = 3570.
= 357 /3570 + 350 /3570 + 255 /3570 + 238 /3570 hours
= 1200 /3570 hours
= 120 /357 hours
= 40 /119 hours
The 8 laps were 40 miles, and using Speed = Distance ÷ Time:
average speed = 40 ÷ (40 /119 )
average speed = 40 x (119 /40 )
= 119 mph
Puzzle 3
Yesterday I was asked to buy some stamps.
In the land of BrainBashers, stamps are available in denominations of 4p, 5p, 7p, 12p, and 19p (just the five different values).
For three denominations of stamps, I was asked to buy six of each. For the other two denominations. I was asked to buy ten of each.
Unfortunately, I forgot which I was supposed to buy six of, and which to buy ten of!
Luckily I had been given the exact money required to buy the stamps, £3.50, so the shopkeeper was able to work out the stamps I needed.
Which stamps did I have to buy?
Puzzle Copyright © Kevin Stone
workings
hint
answer
print
Share link: https://www.brainbashers.com/ puzzle/zknw
Hint
I bought at least 6 of each stamp.
Answer
Six lots of 4p, 7p. and 19p, and ten lots of 5p and 12p.
Reasoning
For three denominations of stamps, I was asked to buy 6 of each, and for the other two denominations, I had to buy 10 of each.
So I had to buy at least 6 of all five denominations.
This would be for a total of 6 x (4 + 5 + 7 + 12 + 19) = 282p = £2.82.
The remaining 68p has to buy the remaining 8 stamps, 4 of each of the two remaining denominations.
If we just bought 1 of each of the two remaining denominations they would have cost 68 ÷ 4 = 17p.
So the two remaining denominations must have been 5p and 12p.
Double-Checking
6 x 4 = 24
10 x 5 = 50
6 x 7 = 42
10 x 12 = 120
6 x 19 = 114
For a total of 24 + 50 + 42 + 120 + 114 = 350p = £3.50.
Puzzle 4
Using the letters AAEEHHLLLLMMNNOOSSTT complete this grid. The grid reads the same across as down.
Note: this puzzle is not interactive, and the squares cannot be clicked.
Puzzle Copyright © Kevin Stone
workings
hint
answer
print
Share link: https://www.brainbashers.com/ puzzle/zkqk
Hint
The bottom word begins with M.
Answer
C
H
A
S
M
H
E
L
L
O
A
L
I
E
N
S
L
E
P
T
M
O
N
T
H
next >
Note: BrainBashers has a Dark Mode option. For BrainBashers, I'd recommend not using your browser's built-in dark mode, or any dark mode extensions (sometimes you can add an exception for a specific website).