Question

If $9^{8.6}\times 8^{3.9}\times {72}^{4.4}\times 9^{3.9}\times 8^{8.6}={72}^x$, then value of $x$ is:

• A. $15.1$
• B. $17.9$
• C. $20.9$
• D. $16.9$

Answer 1

The correct option is D $16.9$

Consider, $9^{8.6}\times 8^{3.9}\times {72}^{4.4}\times 9^{3.9}\times 8^{8.6}$
= $9^{8.6+3.9}\times 8^{3.9+8.6}\times {72}^{4.4}$
= $9^{12.5}\times 8^{12.5}\times {72}^{4.4}={(9\times 8)}^{12.5}\times {72}^{4.4}$
= ${72}^{12.5}\times {72}^{4.4}={72}^{16.9}$
$\therefore x=16.9$