Guess which Izumi!

In how many different ways can you can write the word "Izumi" if you start with the red central letter 'I'?


To enlarge the image above, click here .


The answer is 60.

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3 solutions

Milan Milanic
Mar 16, 2016

Solution:

Go on letter 'Z' to the left. From there, you can go either left, down or up, on a letter 'U'.

If left 'U' is chosen, there are 3 different ways to finish word if 'M' to the left is chosen, if down 'M' is chosen there are 2 ways, that is the same with upper 'M'. Meaning, 7 ways for that left 'U'.

Now, if upper 'U' is chosen there are 4 ways to finish it. It is completely similar for down 'U'. Both of them united, 8 ways.

Since all previously mentioned ways started with left 'Z' (15 ways), solution is obtained when multiplied with 4 (since it is the same if down, up or right 'Z' is chosen). The answer is 60 \boxed{60}

Ah, I initially thought it was 4 × 3 × × 3 × 3 4 \times 3 \times \times 3 \times 3 , because each time you move right there are 3 options to take. That might be a common mistake that others make.

Calvin Lin Staff - 5 years, 2 months ago

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To tell you the truth, I did the same mistake when I was counting it for the first time :)

Milan Milanic - 5 years, 2 months ago
Tran Quoc Dat
Apr 16, 2016

We can use the classical "walking on a rectangular grid" problem to solve:

This is a quarter of the image. 'Cause the image is symmetric, we can calculate in a quarter and then multiply it by 4 4 .

Starting from letter 'I', we need 4 4 steps to reach the last 'I'. In each step, there are 2 2 ways: up or right.

So the number of 'IZUMI's are 2 4 = 16 2^4=16 . Multiply by 4 4 gives us 64 64 .

But, 4 4 words 'IZUMI's are duplicate, which are, the vertical and horizontal ones. We need to subtract by 4 4 .

The answer is 60 \boxed{60} .

Aries Yuangga
Apr 8, 2016

vertical = v

horizontal = h

v or h : 1

vh : 3

hv : 3

vhv : 3

hvh : 3

hvhv : 1

vhvh : 1

sum = 15

total = 15*4 = 60

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