x
=
4
Every step shown. Once you become used to doing this you will almost be able to do the basic one's in your head without writing much down.
Explanation:
Let the unknown value be
x
Converting the words into numbers:
First part: "15 times a certain number" →
15
x
Second part: "plus 5 times the same number"
→
15
x
+
5
x
The last part: " is 80" -> 15x
+
5
x
=
80
We are counting x
'
s
. 15 of them plus another 5 of them gives a total of 20.
So 15
x
+
5
x
=
20
x
=
80
Divide both sides by 20
20
x
÷
20
=
80÷
20
20/20x=80/20
x=4
