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Gita starts from point A and walks 1000 m east. She then walks 800 m north, followed by 640 m west and 512 m south, reaching point B. After this, she continues moving in the same cyclic order: east, north, west, south, with each successive movement 20% shorter than the previous one. After infinitely many such moves, approximately how far in meters will Gita be from her starting point A?

Solution

Correct Option: 4

Each move is 0.80.8 times the previous one, cycling through East, North, West, South. The first four moves are:

East =1000= 1000, North =800= 800, West =640= 640, South =512= 512

After every four moves, the pattern repeats, scaled by (0.8)4=0.4096(0.8)^4 = 0.4096.


So each direction's distances form a geometric progression with common ratio 0.40960.4096, and the common denominator for each sum is:

10.4096=0.59041 - 0.4096 = 0.5904


Net eastward displacement (East minus West):

10006400.5904=3600.5904\dfrac{1000 - 640}{0.5904} = \dfrac{360}{0.5904}

Net northward displacement (North minus South):

8005120.5904=2880.5904\dfrac{800 - 512}{0.5904} = \dfrac{288}{0.5904}


Distance from AA:

d=3602+28820.5904d = \dfrac{\sqrt{360^2 + 288^2}}{0.5904}

3602+2882=129600+82944=212544360^2 + 288^2 = 129600 + 82944 = 212544

212544461.02\sqrt{212544} \approx 461.02

d461.020.5904780.87d \approx \dfrac{461.02}{0.5904} \approx 780.87


Gita is approximately 781781 m from AA.

Answer =781= 781

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