Puzzle 197
Yesterday I was asked to buy some stamps.
In the land of BrainBashers, stamps are available in denominations of 3p, 9p, 11p, 17p, and 21p (just these five different values).
For three denominations of stamp I was asked to buy eight of each, and for the other two denominations I was asked to buy nine of each.
Unfortunately, I forgot which I was supposed to buy eight of, and which to buy nine of!!
Luckily I had been given the exact money required to buy the stamps, £5.00, so the shopkeeper was able to work out the stamps I needed.
Which stamps did I have to buy?
Puzzle Copyright © Kevin Stone
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Hint
I bought at least 8 of each stamp.
Answer
Eight lots of 11p, 17p and 21p, and nine lots of 3p and 9p.
Reasoning
For three denominations of stamp I was asked to buy 8 of each, and for the other two denominations I had to buy 9 of each.
So I had to buy at least 8 of all five denominations.
This would be for a total of 8 x (3 + 9 + 11 + 17 + 21) = 488p = £4.88.
The remaining 12p has to buy the remaining 2 stamps, which must have been 3p and 9p.
Double-Checking
9 x 3 = 27
9 x 9 = 81
8 x 11 = 88
8 x 17 = 136
8 x 21 = 168
For a total of 27 + 81 + 88 + 136 + 168 = 500p = £5.
Puzzle 198
After a day picking strawberries, I ended up with a full basket, which is always nice.
I ate 5, and then gave Alex half of the remaining.
I ate another 3, and then gave Billie one third of the remaining.
I ate another 6, and then gave Charlie two thirds of the remaining.
I now had 34 strawberries left. How many did I start with?
Puzzle Copyright © Kevin Stone
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Hint
Try working backwards.
Answer
335 strawberries.
Reasoning
Working backwards …
I ended up with 34 strawberries, so I had 102 before giving Charlie two thirds.
I ate 6 myself, so I had 108 before I ate those.
I had 108 strawberries, so I had 162 before giving Billie one third.
I ate 3 myself, so I had 165 before I ate those.
I had 165 strawberries, so I had 330 before giving Alex one half.
Ate 5 myself, so I had 335 before I ate those.
Therefore, I started with 335 strawberries.
Double-Checking
I started with 335.
I ate 5, leaving 330.
I gave Alex half (165), leaving 165.
I ate 3, leaving 162.
I gave Billie one third (54), leaving 108.
I ate 6, leaving 102.
I gave Charlie two thirds (68), leaving 34.
Puzzle 199
A large freshwater reservoir has two types of drainage system. Small pipes and large pipes.
6 large pipes, on their own, can drain the reservoir in 12 hours.
6 small pipes, on their own, can drain the reservoir in 18 hours.
How long will 6 large pipes and 6 small pipes take to drain the reservoir?
Puzzle Copyright © Kevin Stone
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Hint
How many reservoirs can each drain in 36 hours?
Answer
7 hours and 12 minutes.
Reasoning
We can use a time that 12 hours and 18 hours both fit in to, in 36 hours:
6 large pipes can drain 3 reservoirs.
6 small pipes can drain 2 reservoirs.
Therefore, together, 6 large and 6 small pipes can drain 5 reservoirs.
36 hours ÷ 5 = 7.2 hours for one reservoir.
7.2 hours = 7 hours and 12 minutes for one reservoir.
Puzzle 200
What comes next in the sequence:
red · orange · yellow · green · blue · indigo · ?
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Hint
A very common sequence.
Answer
Violet.
From the colours of the rainbow.
