Godly ways to get back !

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Four buildings - A A , B B , C C and D D are connected with different paths. You are currently standing at A A .

How many ways are there for you to get to D D and back to A A ?


The answer is 441.

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2 solutions

Priyansh Sangule
Dec 30, 2013

First of all we check out the number of ways from A A to D D .

From A A to C C via B B there are : 3 × 3 = 9 3 \times 3 = 9 ways

Hence, from A A to C C there are: 9 + 1 = 10 9 + 1 = 10 ways

Now, from A A to D D via C C and B B we have: 10 × 2 = 20 10 \times 2 = 20 ways

Hence, from A A to D D there are: 20 + 1 = 21 20 + 1 = 21 ways

Now, Similarly we'll have 21 21 ways back to A A .

Thus, there will be 21 × 21 = 441 21 \times 21 = 441 ways from A A to D D and back to A A .

ANSWER : 441 \boxed{441}

Lokesh Sharma
Dec 31, 2013

F o r A > B > C > D : t h e r e a r e 3 × 3 × 2 = 18 w a y s F o r A > C > D : t h e r e a r e 1 × 2 = 2 w a y s F o r A > D : t h e r e a r e 1 w a y s = 1 w a y F o r t o t a l t h e r e a r e : 18 + 2 + 1 = 21 w a y s f r o m A > D F o r b a c k D > A t h e r e a r e t h e s a m e 21 w a y s S o f r o m A > D a n d t h e n D > A : t h e r e a r e 21 × 21 = 441 w a y s For\quad A\quad ->\quad B\quad ->\quad C\quad ->\quad D:\\ \qquad there\quad are\quad 3\quad \times \quad 3\quad \times \quad 2\quad =\quad 18\quad ways\\ For\quad A\quad ->\quad C\quad ->\quad D:\\ \qquad there\quad are\quad 1\quad \times \quad 2\quad =\quad 2\quad ways\\ For\quad A\quad ->\quad D:\\ \qquad there\quad are\quad 1\quad ways\quad =\quad 1\quad way\\ For\quad total\quad there\quad are:\\ \qquad 18\quad +\quad 2\quad +\quad 1\quad =\quad 21\quad ways\quad from\quad A\quad ->\quad D\\ \\ For\quad back\quad D\quad ->\quad A\quad there\quad are\quad the\quad same\quad 21\quad ways\\ \\ So\quad from\quad A\quad ->\quad D\quad and\quad then\quad D\quad ->\quad A:\\ \qquad there\quad are\quad 21\quad \times \quad 21\quad =\quad \left\lceil 441 \right\rceil \quad ways

That's Right !

Priyansh Sangule - 7 years, 5 months ago

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