Question

The weight of 72 books is 9kg. (a) find the weight of 80 such books. (b) how many books would weight 6kg?

Answer 1

As given 72 books weigh 9kg.
Then find the average weight of a book.
= Total weight/Total books
= 9/72
= 1/8 kg or 0.125 kg

Hence weight of a single book is 0.125kg.

(a) Weight of 80 books = 80 × weight of single book
= 80 × 0.125
= 10 kg

(b) No. of books weighing 6 kg = 6 kg ÷ Weight of single book
= 6 ÷ 0.125
= 48 books.

Answer 2

(a) The weight of 72 books is 9 kg

==> The weight of one book is 9 kg / 72 .....................(1)

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

Hope it helps you

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