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Six X’s have to be placed in the squares of figure below in such a way that each row contains at least one X. In how many different ways can this be done.

Six X’s have to be placed in the squares of figure below in such a way that each row contains at least one X. In how many different ways can this be done.

Grade:upto college level

1 Answers

Navjyot Kalra
askIITians Faculty 654 Points
9 years ago
Hello Student,
Please find the answer to your question
As all X’s are identical, the question is of selection of 6 squares from 8 squares, so that no row remains empty. Here R1 has 2 squares, R2 has 4 squares and R3 has 2 squares. The selection scheme is as follows
R1
R2
R3
1
4
1
or
1
3
2
or
2
3
1
or
2
2
2
∴ Number of selections are
2 C1 x 4 C4 x 2 C1 + 2 C1 x 4 C3 x 2 C2 + 2 C2 x 4 C3 x 2 C1 + 2 C2 x 4 C2 x 2 C2
232-1024_123456.png
Thanks
navjot kalra
askIITians Faculty

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