Question

By which rational number should we multiply 8/21 to get 1?
a -8/21( ) b -21/8( ) c 21/8( ) d 4/21( )
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Answer 1

Answer:

Answer : c) 21/8

Explanation :

Let the other rational number be 's'

s × 8/21 = 1/1

s = 1/1 ÷ 8/21

s = 1/1 × 21/8

s = 21/8

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Answer 2

Given :  The rational number is : $\frac{8}{21}$  

             Its product with an unknown number is : 1

To find : A number by which  $\frac{8}{21}$ should be multiplied to get 1 as the result.

Solution : We can simply solve this mathematical problem by understanding the concept of multiplicative inverse .

Let ,

$\frac{a}{b}$ be a rational number ,

then its multiplicative inverse will be the reciprocal of $\frac{a}{b}$, i.e. $\frac{b}{a}$ .

Note : In order to get 1 as the product of any number, we multiply the number with its multiplicative inverse.

Therefore,

We have our rational number : $\frac{8}{21}$

We must multiply it with its multiplicative inverse $\frac{21}{8}$ to get 1.

Thus,

Our answer will be option C.