Question

The weight of 72 books is 9 kg.
(a) Find the weight of 80 such books.
(b) How many books will weigh 6 kg?​

Answer 1

Answer:

We can solve this problem by Proportions

Step-by-step explanation:

(a) Weight of 80 books

Weight (in kg)       No. of books

9 kg                       72

x kg                       80

9 : x :: 72 : 80

By multiplying the first and last and the middle ones. We get,

9 × 80 = 72x

9 × 80 / 72 = x

10 = x

So, the weight of 80 books is 10 kg

(b) How much books would weigh 6 kg

Weight (in kg)             No. of books

9 kg                             72

6 kg                             x

9 : 6 :: 72 : x

By multiplying the first and last and the middle ones. We get,

9x = 72 × 6

x = 72 × 6 / 9

x = 8 × 6

x = 42

So, the weight of 42 books will be 6 kg

Answer 2

(a) The weight of 72 books is 9 kg

==> The weight of one book is 9 kg / 72

The weight of 80 books is 9 kg / 72 * 80

==> 9 kg / 72 * 80

==>  9 kg / 9 * 10

==> 1 kg * 10

==> 10 kg

The weight of 80 books is 10 kg

(b) The weight of one book is 9 kg / 72  [ From (1) ]

Let x books weigh  6 kg

Now x books weigh 9 kg / 72 * x

According to the problem:

9 kg / 72 * x = 6 kg

==> 9  x / 72  = 6

==> x = 6 * 72 / 9

==> x = 6 * 8

==> x = 48

The number of books are 48

( * this mark means multiplication sign )  

hope this helps u