Question 12
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The street grid below is 4 blocks by 4 blocks. Routes go from A to B, moving only right or up.
The junction X is closed. How many shortest routes from A to B avoid X?
- A 36
- B 70
- C 34 Correct
- D 35
Correct Answer: Option C
All routes: 8C4 = 70
Through X: 4C2 × 4C2 = 36
Avoiding X = 70 − 36 = 34
Trap: 36 is the number through X.
Answer: 34
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