addition
to join numbers or quantities
  
+
=
difference
the amount that remains after one quantity is subtracted
from another quantity
9–3=6
6 is the difference between 9 and 3
doubles
addition facts with two addends that are the same
6 + 6 = 12
Height
height
a measurement of distance
from bottom to top
length
the distance from one point to another
measure
use units to determine size or quantity
subtraction
the difference or range between two numbers
7 -3=4
tally mark
a mark used to keep track of a quantity