1) The document describes a lesson on using a pan balance to determine the weight of unknown objects by adding and removing objects of known weight from both pans until they balance. 2) Students model pan balance problems using variables to represent unknown weights and solve for the variables. 3) The equal sign represents balance, with quantities on either side being equal, like balancing a scale. Letters can be used as variables to represent unknown quantities.

1. MATH
By: Claudia Martinez
4th grade

2. OBJECTIVE:
Students find the weight of a given object by adding or removing objects of known
weight from both pan of a pan balance. They model pan-balance problems using
variables to represent the objects.
 Examples: If the square weighs the same as
the load at the left of the balance, how much
wil the…..
The square weighs ?
 This is a pan balance or
scale. Things go into the two
"pans", and the heavier pan will
go down, like in a seesaw.
 The pentagons weighs:
 If the two things weigh the
same, the balance stays
balanced.

3.  a. One pentagon weighs _____
UNKNOWN SHAPES
If there are "unknown shapes"
on both sides, use this "trick":
a. One rectangle weighs _____
 One circle weighs _____
Take away the same amount of
unknown shapes from both
sides.
The scale WILL continue to
stay balanced! Take away two
diamonds from both sides.
Then we see that three
diamonds weigh 15.

4. In mathematics, the equal
sign "=" is like a scale a. 78 + _m__ = 148
that is balanced. 160 = _k__ + 90
Something is on the right 50 – ___ = 32
side, b. 7 + 6 + 6 = ____ – 10
and something is on the 5 + 5 + 5 + ___ = 2 × 12
left side, and they are 16 + 19 = 2 × ____ + 1
equal or "balanced" c. 2 × 50 = 40 + ____
5+7=2×6 7 × 6 = 2 × ____
4 × 6 – 7 = 2 × ____ + 1
You can use letters as variables to
represent the unknown.