Puzzle 217
In Farmer Stone's hay loft, there were several animals, in particular birds, mice, and cockroaches. One day, feeling bored, I decided to count the animals.
I found there were exactly 150 feet and 50 heads in total, and there were twice as many cockroaches as mice.
How many of each animal were there?
Puzzle Copyright © Kevin Stone
workings
hint
answer
print
www.brainbashers.com
/puzzle/zvyu
share
Hint
Cockroaches have 6 feet, mice have 4, and birds have 2. They all have one head!
Answer
35 birds, 5 mice, and 10 cockroaches.
Reasoning
Cockroaches have 6 feet, mice have 4, and birds have 2. They each have one head.
We can write down expressions for the heads and the feet, calling birds B, mice M, and cockroaches C.
Counting the heads:
(1) B + M + C = 50
Counting the feet:
(2) 2B + 4M + 6C = 150
We are told that for every mouse there are two cockroaches so, C = 2M. Update (1) and (2) to give:
(3) B + 3M = 50
(4) 2B + 16M = 150
If we double (3) we get:
(5) 2B + 6M = 100
We can now do (4) − (5) to give:
10M = 50
M = 5
So, we have 5 mice (and 10 cockroaches).
We can use M = 5 in (3) to give:
B + 3 x 5 = 50
B + 15 = 50
B = 35
So, C = 10, M = 5 and B = 35.
Double-Checking
10 cockroaches have 10 heads and 60 feet.
5 mice have 5 heads and 20 feet.
35 birds have 35 heads and 70 feet.
The total number of heads = 10 + 5 + 35 = 50.
The total number of feet = 60 + 20 + 70 = 150.
Puzzle 218
I recently gave a new carriage clock to my friend for a very special birthday.
However, as usual with my presents, it was quite useless as it loses 6 minutes every hour.
I set it using my own accurate clock at midnight, and the clock now shows 10:12am.
I know that it stopped 2 hours ago, so what is the correct time now?
Puzzle Copyright © Kevin Stone
workings
hint
answer
print
www.brainbashers.com
/puzzle/zhbl
share
Hint
How many clock minutes pass in a real hour?
Answer
1:20pm.
Reasoning
The clock now shows 10:12am, so we know that 10 x 60 + 12 = 612 clock minutes have passed.
Since the clock is losing 6 minutes every hour, for every real hour that has passed, the clock will show 54 minutes.
So, 612 ÷ 54 ≈ 11.33 real hours have passed.
This equals 680 minutes, which is 11 hours and 20 minutes = 11:20am.
The clock stopped 2 hours ago, therefore the time must now be 1:20pm.
Puzzle 220
Place a horizontal or a vertical line into every blank square.
Each number tells you the total length of the lines connected to that square.
Puzzle Copyright © Johan de Ruiter
workings
hint
answer
print
www.brainbashers.com
/puzzle/zflf
share
Hint
Start by looking at the 6 and 4 on the top row.
Answer
next >