Bunuel
A 16-step path is to go from (-4,-4) to (4,4) with each step increasing either the x-coordinate or the y-coordinate by 1. How many such paths stay outside or on the boundary of the square \(-2 \leq x \leq 2\), \(-2 \leq y \leq 2\) at each step?
A. 92
B. 144
C. 1,568
D. 1,698
E. 12,800
Hi
globaldesiAs
Bunuel too has mentioned, it is hard and I would say it is even hard for the standards of Indian CAT as it will take some time.
But I will solve it underneath, some point may be useful in some other question.
First point - In m*n board, the ways to reach from left bottom corner to opposite corner moving up or right is \(\frac{(m+n)!}{m!n!}\)
So here we have to reach from (-4,-4) to (4,4), that is 8*8 board, so straight \(\frac{(8+8)!}{8!8!}\), but the restriction is the path cannot be inside the BLUE square. 8*8 is like a chess board, so ill take an image of chess board and work over it. The brown lines are x-axis and y-axis.
So we have to go into three cases..
(I)
Case I - A to B and then B to T... A to B - \(\frac{(6+0)!}{6!0!}=1\), and B to T - \(\frac{(2+8)!}{8!2!}=45\).. Total 1845=45.
(II)
Case II - A to C and then C to T... A to C - \(\frac{(6+1)!}{6!1!}=7\), but subtract one of case I, that is A to B to C, so 7-1=6 , and C to T - \(\frac{(2+7)!}{7!2!}=36\).. Total 6*36=216.
(II)
Case III - A to D and then D to T... A to D - \(\frac{(6+2)!}{6!2!}=28\), but subtract 1+6 of case I and case II, that is 28-7=21 , and C to T - \(\frac{(2+6)!}{6!2!}=28\).. Total 21*28=588
Total 45+216+588=849
The above was from the left of the blue box, but similar number of ways will be from below the blue box, so another 849.
TOTAL = 2*849=1698.
D
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