Join the Car Talk Community!

The Mathmatical Mystery of 4s

The Puzzler

RAY: This was from my number 4 series. There's an old puzzler from long, long ago, and it went like this: Take the number 4, and using it five times, write a mathematical expression that will give you the number 55. Now it's pretty challenging because 4's an even number and 5's an odd number. How do you get 55 out of five 4's? And the answer is 44 + 44/4.

Jim Adams suggested something a little more challenging. He says, 'Take the number 4, use it 3 times, and write a mathematical expression that will give you the number 55.'

Now you can use any of the mathematical terms that are usually used in writing mathematical expressions: plus sign, minus sign, multiplication, division, square root -- you can't square anything because you'd be introducing the number 2 then. You can only use 4s. Your expression could have any of the symbols. You could have 4 to the 4th, you could have 4 factorial, you could have 4.4. You can use anything that you'd see in a mathematical expression as fair game.

What's the equation?

Think you know? Drop Ray a note!

[ Car Talk Puzzler ]

Support for Car Talk is provided by:

Donate Your Car,
Support Your NPR Station

...and get a tax break!

Get Started

Find a Mechanic

Promo tile

Rocket Fuel