Question

After reading 80\%80% of her e-mails in her inbox, Danette still has MM unread e-mails.

Answer 1

Answer:   The correct options are.....

A)   $\frac{M}{1-0.8}$   and

B)   $5M$

Step-by-step explanation:

Suppose, the number of e-mails Danette had in her inbox before she started reading was $X$.

Percentage of read emails is 80%, so the number of read emails $= (\frac{80}{100}*X)=0.8X$

Thus, the number of unread emails $= X-0.8X=X(1-0.8)$, which is given as $M$.

So, the equation will be........

$X(1-0.8)=M\\ \\ \Rightarrow X=\frac{M}{1-0.8} (Answer: 1) \\ \\ \Rightarrow X=\frac{M}{0.2}\\ \\ \Rightarrow X=(\frac{1}{0.2})M=5M (Answer: 2)$

Thus, the expressions which could represent the number of e-mails Danette had in her inbox before she started reading are:  $\frac{M}{1-0.8}$ or $5M$