Question:
The numerical expression $(3 / 8)+(-5 / 7)=(-19 / 56)$ shows that
(a) rational numbers are closed under addition.
(b) rational numbers are not closed under addition.
(c) rational numbers are closed under multiplication.
(d) addition of rational numbers is not commutative.
Solution:
(b) We have $\frac{3}{8}+\frac{(-5)}{7}=\frac{-19}{56}$
Show that rational numbers are closed under addition.
$\left[\frac{3}{8}\right.$ and $\frac{-5}{7}$ are rational numbers and their addition is $\frac{-19}{56}$ which is also a rational number]
Note The sum of any two rational numbers is always a rational number.
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