Puzzle 17
During a recent BrainBashers race meeting, the fastest driver managed to complete a lap with an average speed of 150 mph.
They managed to complete the first two fifths of the lap at a speed of 123 mph and the second two fifths of the lap at a speed of 164 mph.
At what speed was the final one fifth of the lap length covered?
The answer is not 176 mph.
Puzzle Copyright © Kevin Stone
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Hint
Adding the speeds won't work.
Answer
205 mph.
Reasoning
If we take the number of miles in a lap to be L miles and use Time = Distance ÷ Speed.
The first 2 /5 are covered at 123 mph. Therefore, the time taken was [(2 /5 ) x L] ÷ 123 hours.
The next 2 /5 are covered at 164 mph. Therefore, the time taken was [(2 /5 ) x L] ÷ 164 hours.
The last 1 /5 is covered at y mph. Therefore, the time taken was [(1 /5 ) x L] ÷ y hours.
The entire trip is covered at an average of 150 mph, and we can conclude that:
2L 2L L L
————— + ————— + ——— = ———
5x123 5x164 5y 150
Rearranging and simplifying gives:
1 1 2 2
——— = —— - ——— - ———
y 30 123 164
That means that y = 1 ÷ (1 /30 − 2 /123 − 2 /164 )
Using a calculator gives y = 205.
Puzzle 18
What number comes next in this sequence:
3 · 24 · 102 · 312 · 777 · ?
Puzzle Copyright © Kevin Stone
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Answer
1680.
This is n to the power of 5, starting with 2^5 = 32, with the last digit missing, 7^5 = 16807.
Puzzle 19
This is an annoying paragraph, in which you try to work out what is unusual about it. This paragraph has a quandary though. A solitary word has found a way to slink into this paragraph, to fox your fun, by going against all my jazzy plans. What is that word? Don't try to run a utility to assist you, that would spoil all of my attempts to absorb all of your avid skills in this mind-blowing prank.
Puzzle Copyright © Kevin Stone
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Hint
Is there a missing letter?
Answer
Attempts.
This word contains the only letter E in the entire paragraph, notice how every other letter appears at least once.
Although the letters C, E, J, Q, V, X each all appear once, the longer the piece of text the more difficult it is to avoid the letter E.
Puzzle 20
Place all of the digits from 1 to 9 into the circles so that the sum of the numbers in each straight line is the same.
Puzzle Copyright © Cihan Altay
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Hint
Each line adds to 14.
Answer
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