Let a equal 2b + 3c - 5. What happens to the value of a if

Let a equal 2b + 3c - 5. What happens to the value of a if the value of b decreases by 1 and the value of c increases by 2 ?

1. It increases by 4.
2. It increases by 2.
3. It increases by 1.
4. It is unchanged.
5. It decreases by 2. 

Answer

The correct answer is A.

The new value of b is (b - 1), and the new value of c is (c + 2).

Substituting into the expression for a gives

2(b - 1) + 3(c + 2) - 5

= 2b - 2 + 3c + 6 - 5

= 2b + 3c - 1

Because you are looking for the change in a, write this expression in terms of the original expression for a.

= (2b + 3c - 5) + 4.

So, value of a is increased by 4.