Simplify these expressions
a) 2a + 5a
b) 12x - 3x
c) 3p + 2p-p

a) The two parts of this expression, +2a and +5a are called terms and

the numbers in front of the variables, +2 and +5 are called coefficients.

Because the variables, a and a, are identical,

the two terms in this problem are called like terms.

Like terms can be added together by simply adding their coefficients.

So in this problem, since 2 + 5 is 7, 2a + 5a is simply 11a.

b) Since both terms contain an x, we can subtract them.

Also, change the minus to plus a negative.

So we have 12x + -3x which simplifies to 9x.

c) If there is no coefficient in front of the variable, you can give it

a coefficient of 1, so -p can be thought of as -1p.

So we have 3p + 2p -1p which is 4p.