See also the
Dr. Math FAQ:
order of operations
3D and higher
Browse Middle School Algebra
Stars indicate particularly interesting answers or
good places to begin browsing.
Selected answers to common questions:
Direct and indirect variation.
Inequalities and negative numbers.
Positive/negative integer rules.
Solving simple linear equations.
- Simplify an Expression [6/15/1996]
- Simplifying a Fraction -- and Oversimplifying It [03/03/2012]
A student simplifies a fraction by selectively canceling terms. Doctor Peterson compares the algebraic expression before and after such unbalanced steps, revealing how this method does not maintain equality.
- Simplifying an Algebraic Fraction [05/09/2000]
How can I simplify 1 + 1/(x + 1/x)? I can't figure out the common
- Simplifying an Expression [04/29/1999]
Can you help me figure out (x+3)+(4x-7)+(x-20) ?
- Simplifying an Expression [05/04/1999]
How do you simplify 9x - 3x + 7 - 4x + y - 3 ?
- Simplifying Expressions [8/31/1996]
How do I simplify (y + 3) - 2(y + 7) ?
- Simplifying Expressions [01/27/1997]
How do you simplify 3x - 2y - x -3y?
- Simplifying Expressions [11/24/1997]
Solve: 2x - ( 3 - x ) = x - 7 .
- Simplifying Mixed Algebraic Expressions [05/08/1998]
Simplifying fractions such as 2x - (x+y)/y and 4 - 3/(y-1) - 1/(y+1).
- Simplifying Polynomials [4/26/1996]
How do you simplify polynomials?
- Simplifying Using the Distributive Property [09/07/99]
How do you simplify an expression like 12(c+3d+4e) + 2(2c+d+6e)?
- Simplifying with Cube Roots [01/22/1997]
Simplify: cube root(3) / [cube root(6) + cube root(3)]
- Simultaneous Equations [8/25/1996]
Ten percent of the reds were added to twenty percent of the blues, and
the total was 24...
- Simultaneous Equations [08/10/1997]
A, B, and C can finish a job in 6 days... In how many days can each man
working alone do the job?
- Simultaneous Equations [07/01/2002]
A man has a total of 20 dimes and quarters. If the dimes were quarters
and the quarters were dimes he would have 90 cents more than he has
now. How many of each coin does he have?
- Six Chickens, Five Minutes [01/09/2003]
If 1 and 1/2 chickens lay 1 and 1/2 eggs in 1 and 1/2 minutes, how
many eggs will 6 chickens lay in 5 minutes?
- Slope and (x, y) Intercept [02/19/1999]
Does slope depend on (x, y) intercept or does (x, y) intercept depend on
- Slope-Intercept Formula [06/05/2001]
Why does y = mx + b have to be that way?
- Solutions to Equations [01/16/1997]
How do you make a table of values of x and y that make the equation 3/4y
= -x true?
- Solution Using Verbal Argument and Model [02/06/2002]
Mr. Li has fewer than 200 sweets. He wants to give each pupil in his
class an equal number of sweets. If he gives each pupil 2 sweets, he will
have 70 sweets left over; if 4, he will need 10 more sweets. How many
pupils are there in the class? How many sweets does Mr. Li have?
- Solve 2x + 3 = 10 [09/17/2001]
I don't understand what to do to simplify the problem.
- Solve for g... [04/08/1997]
I understand -3x+5x+4 = -6 to solve for x, but I don't understand
g+.04g+60 = 8796.
- Solve Using Elimination [01/24/2001]
Solve by using elimination, and check solutions: x+6y=20, x+2y=12.
- Solving a Fraction Problem Using Common Sense [03/21/2004]
When the gun sounded, only two-fifths of the racers began to run. If
460 racers began to run, how many racers were there in all? Can you
show me how to figure out what a fraction is without knowing the total
- Solving a Linear Equation in One Variable [02/27/1998]
Solve for q: -13 - q - 9 = 5q - 9 - q.
- Solving a Math Poem [05/24/2000]
Take five times which plus half of what, and make the square of what
- Solving a Mixture Problem Intuitively and with Algebra [07/06/2007]
There are 7 litres of turpentine in a mixture of 21 litres of water
and turpentine. How many litres of turpentine must be added to make a
mixture of 75% turpentine?
- Solving an Algebraic Equation [12/21/1995]
If x = 2y = 3z = 1,then what is x(y-z)squared + y(z-x)squared + z(x-
- Solving an Equation with two Variables [11/20/1995]
The problem is n + n + 5 = 25. How do I do this? It has two variables.
- Solving a Rational Inequality [11/15/2004]
How do you solve a rational inequality like (x-1)/(x+3) < 3?
- Solving a System of Three Equations in Three Variables [06/23/2007]
How can I find values of x, y, and z that make all three of these
equations true: x + y + z = 10, x - 2y + z = -2, and x - y - z = -12?
- Solving a Typical Rate-Time-Distance Problem [09/02/2005]
A look at how to use algebra to solve problems involving rates, times,
and distances. The problem in this example centers around walking and
running at two different rates for a total of 3 hours.
- Solving Equations [9/3/1995]
If n=x^2+y then how can you work out x if you know n and y, and work out
y knowing n and x?
- Solving Equations [3/23/1996]
A student has a number of 'word problems' that require solving equations.
- Solving Equations [01/15/1998]
Please help me solve these equations: x2+y = 31; y2+x = 41.
- Solving Equations for Variables [02/03/2002]
How do you solve the following equation for (M) and then (m)? k = M-m/
- Solving Equations that Equal Zero [02/26/1997]
How do you solve an equation like (5x+10)(7x-2) = 0?
- Solving Equations to Find Profit [8/10/1996]
You buy A and B for 40,000 Won; sell A for a 0.3 percent and B at a 0.2
percent discount. You profit 5000 Won - what was the original price of A?
- Solving Equations with Square Roots [03/28/2003]
When solving x + 1 = sqrt(x + 3), we can square both sides then solve
the equation; however, we get an extra solution that doesn't work. Why?
- Solving for b [05/10/2000]
When solving 10 + 2*sqrt(b) = 0 we get b = 25, but when we insert 25 into
the equation, we end up with 20 = 0. What are we doing wrong?