Question

the product of two rational number is -21/8. If one of the numbers is 4/5. find the another number​

Answer 1

Answer:

It's answer will be -105/32

Answer 2

Given that product of two rational numbers is  $\frac{-21}{8}$, in which one of the number is  $\frac{4}{5}$.

We need to find another rational number.

As we know  "A rational number has the form of p/q, with p and q being integers and q being a non-zero denominator."

Let us assume the  unknown number as $\frac{x}{y}$      (where $y\neq 0$)

So,  $\frac{x}{y}*\frac{4}{5}=\frac{-21}{5}$

      $\frac{x}{y}*\frac{4}{5} *\frac{5}{4} =\frac{-21}{8} *\frac{5}{4}$       (Multiplying both sides with $\frac{5}{4}$)

      $\frac{x}{y} =\frac{-21}{8} *\frac{5}{4}$          (∵ $\frac{a}{b}*\frac{c}{d}=\frac{ac}{bd}$)

      $\frac{x}{y} =\frac{-105}{32}$

      $\frac{x}{y} =\frac{-105}{32}$

Therefore, the other rational number is  $\frac{-105}{32}$.