Answer:
169 letters
Step-by-step explanation:
Given:
He moves 90 letters from his INBOX to his OUTBOX.
After moving it is down to 79 letters in the INBOX and up to 156 letters in the OUTBOX.
Question asked:
Before he moved the letters, how many were in the INBOX ?
Solution:
Let initially letters having in the INBOX = [tex]x[/tex]
According to question:-
As he moved the 90 letters from his INBOX to his OUTBOX, we will write this as:
Initially letters having in the INBOX - Letters mover from = 79
[tex]x-90=79\\[/tex]
Adding both side by 90
[tex]x-90+90=79+90\\x=169[/tex]
Therefore, before he moved the letters, there were 169 letters in the INBOX.