Tetromino Grid!!

Find the number of ways of arranging the above five types of tetro-minoes in a 5×4 grid using each piece exactly once. A square in the grid can be occupied by atmost one piece.


This question is not original .

0 6 4 1 5 2 7 3

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3 solutions

Aryan Sanghi
Jun 22, 2020

Here is an observation

All the tetro-minoes have to fit neatly inside the grid as the sum of number of squares of tetro-minoes is 20 which is equal to number of squares in the grid.


Let's colour each square in the grid alternatively by White and black like a chess board.

So, we'll have an equal number of white and black squares.


So, similarly we also have to colour have each square of the tetro-minoes alternatively white and black.

So, we can see that combining all tetro-minoes, we get unequal number of black and white squares.

So, they can't fit neatly in the grid.

So, there are 0 \boxed{0} ways.

Simply, if we take the fourth piece and try to fix it in its possible places then there would be 1 or some squares left near it as the other shapes cannot fit into.

Try my solution and please upvote it. @Siddharth Chakravarty .

Aryan Sanghi - 11 months, 3 weeks ago

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Yes, I did! Very nice way of thinking of the patterns?

Siddharth Chakravarty - 11 months, 3 weeks ago

these types of solutions aren't rigorous because maybe there's a way to fit the other shapes into those squares but you're not smart enough to find it

Lowell Chen - 11 months, 1 week ago
Vikram Karki
Jun 22, 2020

good problem

can be converted into 4 * 4 grid after terminating the tower like piece.

PS : by the way what is it called(the tower like piece)

Thanku @Vikram Karki .

Aryan Sanghi - 11 months, 3 weeks ago

But, it's not my question.

Aryan Sanghi - 11 months, 3 weeks ago

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yep, you mentioned it in the problem. but you shared with us.

Vikram Karki - 11 months, 3 weeks ago

it's called the i-block in tetris

Lowell Chen - 11 months, 1 week ago

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thank you sir

Vikram Karki - 11 months, 1 week ago

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no problem

Lowell Chen - 11 months, 1 week ago

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