Question

Weight of 72 books is 9kg. What is the weight of 42 such books

Answer 1

Answer:

72 books weight ===== 9kg

1 book weight ======= (9/72)kg

42 books weight ===== (9/72)*42 = 5.25 kg (Ans)

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Answer 2

• Given weight of 72 kg books are 9 kg

So the Question is about to find the total weight if 42 such books ✓

we can calculate the total weight of 43 such books by using the unitary method ✓

Let us find the weight of the given quantity of books by applying the unitary method

$\bold{given \: 72 \:books = 9 \: kg }$

$\\ \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: = > 72 books\: \: \: = 9 \\ \\ \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: = > \: so \: 1 \: book \: \: = \frac{9}{72} \\ \bold {therefore} \\ \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: = > \: 42 \: books \: = \frac{9}{72} \times42 = \frac{378}{72} = 5.25 \: kg$

So by applying the unitary method we calculated that the cost of 42 books is equivalent to approx 5.25 = Rs 6✓

The general rule of unitary method is

$if \: x \: quantity \: = rs \:1 \\ so \: 1 \: such \: quantity \: = \frac{1}{x} \\ \red {therefore \: required \: quantity \: = \frac{1}{x} \times required \: given \: quantity \: to \: find \: \: }$