Nanyang Pri Sch P6 CA1 2008 Math Q45

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.