Question

After reading 80% of her e-mails in her inbox, Danette still has M unread e-mails. Which of the following expressions could represent the number of e-mails Danette had in her inbox before she started reading? Choose 2 answers: (Choice A) 5M (Choice B) 1.8M (Choice C) 80M (Choice D) 0.8 M ​ (Choice E) 1−0.8 M ​

Answer 1

(Choice A) 5M

Explanation:

Let total no. of e-mails in inbox be x

Since she read 80 % of mails i.e 80 % of x

⇒
`80\% * x`

⇒
`(80)/(100)* x`

⇒
`0.8 x`

So, she read 0.8x e-mails.

So, remaining email = total e-mails - read e-mails

`=x-0.8x`

Since we are given that Danette still has M unread e-mails.

⇒
`M=x-0.8x`

⇒
`M=x(1-0.8)`

⇒
`M=x* 0.2`

⇒
`(M)/(0.2)=x`

⇒
`(10M)/(2)=x`

⇒
`5M=x`

Thus the expression represent the number of e-mails Danette had in her inbox before she started reading is 5M.

Hence Choice A is correct.