Which expression can be substituted for x in the top equation of the system below to solve the system by substitution?

2x + 10y = 1
x – 4y = –4


1. 4y – 1
2. y – 4
3. 4y – 4
4. 4 – 4y

I need some help with substition, here is a problem.. can you help me work through it. Please don't give me the answer, just tell me what I have to do. I tried putting them all into the equation, but the answers I get are not logical, I am so confused!

Solve Equations by Substitution (with worked solutions & videos)

Get x on your x - 4y = 4 equation alone. Then substitute that into the top equation where you see X. Combine the like terms and solve.

good luck!

Would it end up being 4y-4?

Right! :)

In fact, in substitution, you need to substitute a term by an expression.

Say x = y + 1
x = -2y + 2

You will use the fact that x is also equal to -2y + 2 to solve the first equation. From this example, you know that x = y + 1, but is also equal to -2y + 2. This gives:

y + 1 = -2y + 2

This time, there is only one variable, hence, is easily solved.

Say now, if I turned the second equation around, this gives: x + 2y = 2.

x = y + 1
x + 2y = 2

Do you realise that it's the same problem, but only 'twisted' in another way?