Question: Help me write the following as an equation? four-fifths is 3 more than the opposite of a number.
Well equations have unknowns, or variables.
It looks like the unkonown variable in your equation is a number, some number or other.
Let's call the number N.
Now see if we can build up the equation.
The first thing it says is: four-fifths is 3 more than ...
That means: four-fifths of N is 3 more than ...
When two numbers have the same magnitude but are opposite in sign, then they are called opposite numbers.
So if M is the opposite number to N then M = -N.
The complete phrase is: four-fifths is 3 more than the opposite of a number.
i.e. four-fifths of N is 3 more than M.
or (4/5)*N = M + 3 (the rhs means 3 more than the opposite of N)
i.e. (4/5)N = -N + 3 -- multiply both sides by 5
4N = -5N + 15 -- add 5N to both sides
9N = 15 -- divide both sides by 9
N = 5/3