Multiple choice general knowledge math & puzzles

A shop stores x kg of rice.The first customer buys half this amount plus half a kg of rice.The second customer buys half the remaining amount plus half a kg of rice.Then the third customer also buys half the remaining amount plus half a kg of rice.Thereafter, no rice is left in the shop.Which of the following best describes the value of x?

  1. 2<=x<=6

  2. 5<=x<=8

  3. 9<=x<=12

  4. 13<=x<=18
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Working backwards: after 3rd customer, 0 kg remains. Before 3rd: 0.5 + 0.5 = 1 kg. Before 2nd: 1/2 + 0.5 = 1 kg. Before 1st: 1/2 + 0.5 = 1 kg. Therefore x = 1.75 kg, which falls in range [5,8]. Forward check: Start with 7, after 1st: 7 - 3.5 - 0.5 = 3; after 2nd: 3 - 1.5 - 0.5 = 1; after 3rd: 1 - 0.5 - 0.5 = 0. The pattern works for x = 7.

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