Logic Puzzles

13. How Many Gloves Guarantee a Pair of Each Color?

A lady keeps gloves and hats in her closet. Among the gloves there are

  • 14 blue gloves
  • 25 red gloves
  • 45 yellow gloves

The light is out and the closet is in total darkness. By touch she can always distinguish a glove from a hat, so she removes an item only if she is certain it is a glove. However, she cannot tell the color of a glove in the dark.

What is the minimum number of gloves she must remove to be certain that she has at least one pair (two gloves) of each color?

  1. 72
  2. 35
  3. 33
  4. 39

Added 19 August 2010

Hint:

Think about the worst-case order in which the colors could appear, and apply the pigeonhole principle.

Solution:

To guarantee two gloves of every color, consider the worst case: try to delay completing one of the color pairs as long as possible.

Suppose blue is the color that is delayed. She could first draw every red and yellow glove plus one blue glove without yet having two blues. That is

25 (red) + 45 (yellow) + 1 (blue) = 71 gloves.

The very next glove she draws must be blue (only blues are left), giving her the second blue she needs. Therefore she must take

71 + 1 = 72 gloves

to be certain of having a pair of each color. Answer: A) 72.


Comments (7)

cat 21 August 2010

A lady has some fine gloves and hats in her closet: 14 blue, 25 red, and 45 yellow. We assume these numbers are the totals of hats and gloves of each color, and that all gloves come in pairs (one left, one right).

In the worst case, each odd total reflects just one hat, and the even total reflects no hats. Then there are 22 yellow pairs, 12 red pairs, and 7 blue pairs of gloves. She must draw 22+12+1=35 left-handed gloves, and similarly, 35 right-handed gloves.

This is 70 gloves in all, but not just any 70 gloves. She can try each glove she draws to see which hand it fits, and add it to the total for that hand. Even if the gloves were fastened together in pairs, she would still need to draw 35 pairs, which is 70 gloves.

s.b. 3 January 2011

14 blue 25red etc...does it include the no of hats????????? or is it just the no of gloves??

bds021 29 May 2011

72
worse case scenario all of the red and yellow items are gloves, then she could take out 70 gloves and they could all be either yellow or red. The next two gloves would have to be blue because everything left in the closet is blue.

Of course this is all assuming there exists a pair of gloves for each color

quiz-master-India 31 March 2015

72

bathfilms 14 July 2016

SOLUTION PART 1)
I reckon the maximum answer is 75 gloves

Remember from the question: "... that ALL gloves come in PAIRS (one left, one right). "

So, if there are 45 yellow items, the maximum number of yellow gloves is 44 plus 1yellow hat
And if there are 25 red items, the maximum number of red gloves is 24 + 1 red hat
If there are hats of all 3 colours, then the maximum number of blue gloves is 12 + 2 blue hats

SOLUTION PART 2)
Worst case scenario (i.e. maximum number of gloves removed before a pair of each is guaranteed):

She could take out 44 yellow gloves, then 24 red gloves = 68 to guarantee

Then she must take out 7 blue to guarantee a blue pair

Total = 68 + 7 = 75

SOLUTION PART 3)
Assuming that the question is not flawed, and given that 75 is not a given answer, then the person setting the question knows that there must be more hats. To maintain PAIRS of gloves (as stated there are), then the increase in hats must be even too.

SOLUTION PART 4)
To reduce the answer from 75 to as low as thirty-something, we need to optimise the reduction in gloves and increase in hats:

Using:
Blue gloves = 2, blue hats = 12
Red gloves = 2, red hats = 23
Yellow gloves = 30 OR 28 OR 34

This would mean, glove removal would be:
30Y + 2B + 2R = 34
OR
28 + 2B + 2R = 32
OR
34 + 2B + 2R = 38
As none of these answers are given, we must turn to the only answer that is an even number...

SOLUTION PART 5)
Using
Blue gloves = 4
Red gloves = 24
Yellow gloves = 44

This could mean, glove removal would be:
44Y + 4B + 24R = 72

This is one of several possible answers, but the only possible one given.
It would also mean that there would be 12 hats: 10 blue, 1 red and 1 yellow.
This would give Answer = 72 gloves would need to be removed.
(But not for the reasons given by others)

However, in reality only 71 would need to be removed:
44Y + 24R + 3B = 71

Hence, I propose that all 4 given answers are invalid.

Therefore I will stick with my original value of 75.

Dzallen 14 July 2016

If we assume there can be any number of R B or Y hats, and left and right gloves are separated, then all four answers are possible:

no. gloves: Y R B
44 24 6 =72 gloves needed
30 10 8 =35 gloves needed
...etc.
I think it's most reasonable to assume all 12,25 and 45 are numbers of gloves, and that there is no difference between left and right gloves, as this means the answer can only be 72.

bathfilms 15 July 2016

Yes, sorry, I just realised that the axiom "... that ALL gloves come in PAIRS (one left, one right)" did not come from the original question, but rather from another reply.

ANSWER = 72

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