[OK]

Privacy Policy  -  Terms & Conditions  -  See Details
We use cookies to personalise content and ads. We also share information about your use of our site with our advertising partners who may combine it with other information you've provided to them or they've collected from your use of their services.

BB Logo Spacer
Spacer
Line
Line

Difficulty: MediumPuzzle Details

Puzzle IconImagine you have one cup of tea and one cup of coffee.

Place a spoonful of the tea into the coffee and stir well.

Then place a spoonful of the tea/coffee mixture back into the tea.

Does the cup of coffee now contain more tea, or the cup of tea more coffee?

[Ref: ZGED]

Show Hint Show Answer Print Puzzle

Answer:
Surprisingly, they are actually the same.

After both swaps have taken place, both cups contain the same amount of liquid that they each started with.

So, any tea missing from the cup of tea is now in the cup of coffee.

The same amount of coffee must be now missing from the cup of coffee, and must be in the cup of tea.

Line

This can also be shown using algebra:

If each cup contains 100 units of its respective beverage and a spoon holds 10 units, then at the start we have:

CoffeeCup = 100 Coffee
TeaCup    = 100 Tea

We now transfer a spoonful of tea across to the coffee to give:

CoffeeCup = 100 Coffee + 10 Tea
TeaCup    = 90  Tea

We now transfer a spoonful of the coffee/tea mixture back to the tea cup, this 10 unit spoonful will contain [10 x (100 Coffee + 10 Tea) / 110]. So we will have:

CoffeeCup = 100 Coffee + 10 Tea - [10 x (100 Coffee + 10 Tea) / 110]
TeaCup    = 90  Tea             + [10 x (100 Coffee + 10 Tea) / 110]

If we simplify this we get:

CoffeeCup = (10000 / 110) Coffee + (1000 / 110) Tea
TeaCup    = (10000 / 110) Tea    + (1000 / 110) Coffee

So there is as much coffee in the tea cup as there is tea in the coffee cup!


Our Favourite Illusions

 Shadow Illusion
Are the squares A and B the same colour?

 Spinning Dancer
Which way is the dancer spinning?

 Impossible Waterfall?
Is the water flowing uphill in this impossible waterfall?

 The Butterfly
A colourful butterfly?

 Duck Or Rabbit?
Is this a duck or a rabbit?

 Hidden Faces
Can you find his three daughters as well?

 Blind Spot
An amazing demonstration of your blind spot.

 Impossible Prongs?
Impossible prongs?

 What Am I?
Can you tell what this is a picture of?

 Who Turned To?
Who is missing?

 Same Eyes?
Are her eyes the same colour?

 Parallel Cafe Wall Lines?
Are the horizontal lines parallel?

 



 

Line


BrainBashers™ is a trademark. We use cookies to personalise content and ads. We also share information about your use of our site with our advertising partners who may combine it with other information you've provided to them or they've collected from your use of their services. For more information please view our privacy policy. By using the site you also agree to our terms and conditions.

Line
Line