• # question_answer28) The weight of 72 books is 9 kg. What is the weight of 40 such books?

Given, weight of 72 books = 9 kg $\therefore$ Weight of 1 book $=\frac{9}{72}kg$ $\therefore$Weight of 40 books $=\frac{9}{72}\times 40kg=\frac{360}{72}kg=\frac{360\div 72}{72\div 72}=5kg$ [$\because$HCF of 360 and $72=2\times 2\times 2\times 3\times 3=72$] Hence, the weight of 40 books is 5 kg.