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From Fitzpatrick - 37(e) - Qu 5:
Figure shows a pattern of suburban roads. In how many ways can a motorist travel from A to X without turning back at any stage?
Ans: 52.
Why is this not 70 ways? Can someone explain how they get 52 please?
My method was: by working back from X, you get pascals triangle set up on the corners. The number at A is 70.
My teachers method: You can either go right or up. To get to X, its any 8 movements in any order of rights/ups. So:
8!/(4!x4!) = 70
What am i missing?
Figure shows a pattern of suburban roads. In how many ways can a motorist travel from A to X without turning back at any stage?
Ans: 52.
Why is this not 70 ways? Can someone explain how they get 52 please?
My method was: by working back from X, you get pascals triangle set up on the corners. The number at A is 70.
My teachers method: You can either go right or up. To get to X, its any 8 movements in any order of rights/ups. So:
8!/(4!x4!) = 70
What am i missing?
