Plug in Technique

Plug In Technique

9. Bob has 4 dollars more than Lisa does. If Lisa has x dollars, how much would Bob have if he doubled
his money.

A) x + 4
B) 2x
C) 2x + 4
D) 2x + 8

1)  Pick a number to use.

2)  Do the problem with your number.

3)  Put the numbers into the choices.

A) x + 4
B) 2x
C) 2x + 4
D) 2x + 8

*If 2 answers work, go back to step 1 and use a different number.

Types of Plug in Problems

1.  Explicit Variables - Having a variable in the answer choices is the first sign of a Plug In problem. *This also works when there is more than one variable.

EX: 15) How many hours are there in d days and h hours?

A)  14h + d

B)  h + 24d

C)  24 ( h + d)

D)  h + d24 *Plug in for each variable independently.

1)  Pick a number to use for each variable.

2)  Do the problem with your numbers.

3)  Put the numbers into the choices.

a.  14h + d

b.  h + 24d

c.  24 ( h + d)

d.  h + d24

EX: 14) If x + 5 is 3 less than y, then x – 2 is how much less than y?

A)  6

B)  7

C)  8

D)  10

*If you have Restrictions on the variable, plug in for one variable and then use the
value to figure out the other variable.

1)  Pick a number to use for each variable.

2)  Do the problem with your numbers.

3)  Which number is the correct answer?.

2.  Implicit Variables

When you have a missing value, you can look at the problem as having an implied variable.

Ex: 33. Larry cuts a piece of paper into two equal pieces. He takes one of those pieces and cuts it into three equal pieces. The area of one of the smallest pieces is what fraction of the area of the original piece of paper?

1)  Pick a number to use for the missing value.

2)  Do the problem with your number.

3)  What number is the correct answer?.

Geometry

15) In the figure above, if y = 90 – x, what is z in terms of x?

A) 90 + x
B) 90 – x
C) 180 + x
D) 180 – x

4)  Pick a number to use for the variable x.

5)  Do the problem with your numbers.

6)  Put the numbers into the choices.

a.  90 + x

b.  90 - x

c.  180 + x

d.  180 - x