**A faulty weighing machine scale showed a reading of 0.2 kg when nothing was placed on it. A box which contained 21 identical books was placed on the weighing scale. After 5/7 of the books were removed from the box, the weighing scale showed a reading of 32.68 kg. Given that the mass of each book was 0.8 times the mass of the box, find the mass of the box.Solution**

Mass of book is 0.8 that of box -----

Book ----- 8 units

Box ----- 10 units

After 5/7 book removed, 2/7 was left:-

(2/7) x 21 books = 6 books

6 books + box ----- 32 680g – 200g

(6 x 8 units) + 10 units ----- 32 480g

58 units ----- 32 480g

1 unit ----- 32 480g divided by 58 = 560g

(Box) 10 units ----- 10 x 560g = 5600g or 5.6 kg

**Answer: The mass of the box was 5.6 kg.**

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