Progressive Countdown

If you’re given a number, subtract 1, then 2 from the result, then 3 from that result and so on until you reach 0 or a negative number.

For example, if you’re given 15:

15 – 1 = 14
14 – 2 = 12
12 – 3 = 9
9 – 4 = 5
5 – 5 = 0

Which of these numbers will finish exactly at zero?

102 103 104 105 106

105

105 – 1 = 104
104 – 2 = 102
102 – 3 = 99
99 – 4 = 95
95 – 5 = 90
90 – 6 = 84
84 – 7 = 77
77 – 8 = 69
69 – 9 = 60
60 – 10 = 50
50 – 11 = 39
39 – 12 = 27
27 – 13 = 14
14 – 14 = 0

Posted in Brain Teasers

Three Kinds of Apples

Three kinds of apples are mixed randomly in a box. How many apples must you take out to be sure of having at least two apples of one kind?

Four. If the apples are A, B, and C, it’s possible that you could take out one A, one B and one C with three apples, but the fourth apple must be one of the three kinds.

Posted in Brain Teasers

Lying On Certain Days of the Week

Angel lies on Mondays, Tuesdays and Wednesdays but tells the truth the rest of the week.

Brenda lies on Thursdays, Fridays and Saturdays, but tells the truth every other day.

Angel says, “Yesterday I was lying.”

Brenda replies, “So was I.”

What day was it?

Thursday.

Putting the information in a table makes it easier to solve. We’ll use A for Angie, B for Brenda, T for truth and F (false) for lying.

  S M T W Th F S
A T F F F T T T
B T T T T F F F

To begin with, there aren’t any days where both of them told the truth and lied the day before, so we know one of them must be lying.

So we have two options, either Angel is lying or Brenda is.

Option 1. Angel is lying.

In order for this to be the case, she needs to be lying today and telling the truth yesterday, so we need two days in a row with T F. And if Brenda is telling the truth, she would need two days with F T. That means we’re looking for two days that have

Angie:  T F
Brenda: F T

Option 2. Brenda is lying.

This is just the reverse of the above, so we need to find:

Angie:  F T
Brenda: T F

The only day that matches either of the two options is Thursday, and it’s option 2. Brenda is the liar.

Posted in Brain Teasers

From Cold To Warm In Four Steps

How do you get from cold to warm in four steps, changing only one letter at a time to form a new word at each step?

cold
cord
word
worm
warm

An alternative is:
cold
cord
word
ward
warm

Yet another option, thanks to Beth:
cold
cord
card
ward
warm

Posted in Brain Teasers

How to Stay Dry?

A group of ten people are going out for pizza but only two of them have an umbrella to keep them dry. Somehow they are able to walk all the way to the pizza place without getting wet. How?

It’s not raining.

Posted in Brain Teasers

Made of Five Letters and Seven Letters

I’m made out of five letters,
And I’m made out of seven letters;
I have keys but I don’t have locks,
I’m concerned with time, but not with clocks.

What am I?

A piano. The word piano has five letters, and the scale on the piano is A through G, seven letters. The piano keys don’t have locks and playing piano requires you to keep time (but with a metronome, not a clock).

Posted in Riddles
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Two Three Ten Sequence

If:
2 3 = 10
7 2 = 63
6 5 = 66
8 4 = 96
9 7 = __

What is the missing number?

f(n, m) = (n + m) × n

e.g. f(2, 3) = (2 + 3) × 2 = 10

Hence, f(9, 7) = (9 + 7) × 9 = 144

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Only Useful When Full

I am only useful when I’m full,
Yet I am always full of holes.

What am I?

A sieve, used for straining food like pasta.

Posted in Riddles

Short Black Dress

In the day I stand tall in a white petticoat. By evening I’m in my short black dress. What am I?

The wick of a candle.

Posted in Riddles

I A N Rebus

What does the following rebus represent?

I           A
      N
R           B

Scatterbrain.

Posted in Riddles
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