Question

Bob installed new windows in his house which were advertised to cut his energy bill by 7.1% per month after installation. If his new energy bill was $315, what was his monthly bill before he installed the new windows?

Answer 1

His monthly bill before he installed the new windows was $339.074...

Explanation

Suppose, his monthly bill before he installed the new windows was  $x$ dollar.

As his energy bill was decreased by 7.1% per month after installation, so the amount of bill decreased $=x*\frac{7.1}{100}=0.071x$ dollar

Given that, his new energy bill was $315. So the equation will be...

$x-0.071x= 315\\ \\ 0.929x=315\\ \\ x=\frac{315}{0.929}=339.074....$

So, his monthly bill before he installed the new windows was $339.074...