Solve for X in the Linear Equation: 3x + 5 = 20

Q: Why do I subtract 5 from both sides first?

You want to isolate the term with x (which is 3x) before dealing with the coefficient. Subtracting 5 first gives you $ 3x = 15 $, which is much simpler than working with fractions!

Q: What if I accidentally add 5 instead of subtracting?

Adding 5 to both sides gives $ 3x + 10 = 25 $, which makes the problem harder! Remember: to undo addition, you must subtract the same number from both sides.

Q: Can I check my answer a different way?

Yes! You can also think about it logically: "What number times 3, plus 5, equals 20?" Since 3 × 5 = 15, and 15 + 5 = 20, the answer is 5.

Q: What if my equation had subtraction instead?

For equations like $ 3x - 5 = 10 $, you'd add 5 to both sides first. The key is using the opposite operation to undo what's being done to x.

Q: Do I always divide last?

When solving $ ax + b = c $ type equations, yes! First handle the constant (b), then divide by the coefficient (a). This order keeps your work clean and simple.

Linear Equations with Isolation Steps

$3x + 5 = 20$

$x = \text{?}$

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Understand the problem

$3x + 5 = 20$

$x = \text{?}$

Step-by-step solution

To solve the equation $3x + 5 = 20$ , follow these steps:

1. Subtract 5 from both sides: $3x = 20 - 5$

2. Simplify the right side: $3x = 15$

3. Divide both sides by 3: $x = \frac{15}{3}$

4. Solve: $x = 5$

Final Answer

Key Points to Remember

Essential concepts to master this topic

Rule: Use inverse operations to isolate the variable term
Technique: Subtract 5 first, then divide: 3x = 15, so x = 5
Check: Substitute back: 3(5) + 5 = 15 + 5 = 20 ✓

Common Mistakes

Avoid these frequent errors

Dividing by the coefficient before removing the constant
Don't divide 3x + 5 = 20 by 3 first = $x + \frac{5}{3} = \frac{20}{3}$ ! This creates messy fractions and makes the problem harder. Always subtract or add constants first, then divide by the coefficient.

Practice Quiz

Test your knowledge with interactive questions

Find the value of the parameter X

$\frac{1}{3}x=\frac{1}{9}$

FAQ

Everything you need to know about this question

Why do I subtract 5 from both sides first?

You want to isolate the term with x (which is 3x) before dealing with the coefficient. Subtracting 5 first gives you $3x = 15$ , which is much simpler than working with fractions!

What if I accidentally add 5 instead of subtracting?

Adding 5 to both sides gives $3x + 10 = 25$ , which makes the problem harder! Remember: to undo addition, you must subtract the same number from both sides.

Can I check my answer a different way?

Yes! You can also think about it logically: "What number times 3, plus 5, equals 20?" Since 3 × 5 = 15, and 15 + 5 = 20, the answer is 5.

What if my equation had subtraction instead?

For equations like $3x - 5 = 10$ , you'd add 5 to both sides first. The key is using the opposite operation to undo what's being done to x.

Do I always divide last?

When solving $ax + b = c$ type equations, yes! First handle the constant (b), then divide by the coefficient (a). This order keeps your work clean and simple.

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