Mental Math Grade 6 Teacher's Guide

• Compensation (Review)
In the development of mental computation skills,
the exercises should be presented with both visual
and oral prompts. This means that individual
practice items should be written on the chalkboard,
overhead, dry-erase board or strips of paper so that
students can see the numbers as well as hear them.
This strategy involves changing one number in a sum to a nearby ten,
hundred, thousand, or decimal tenth or hundredth, carrying out the
addition using that changed number, and then adjusting the answer to
compensate for the original change. Students should understand that
the reason a number is changed is to make it more compatible and
easier to work with. They must also remember to adjust their answer to
account for the change that was made.
Examples
a) For 52 + 39, think,“ 52 plus 40 is 92, but I added 1 too many to take
me to the next 10, so I subtract one from my answer to get 91.”
b) For 345 + 198, think, “345 + 200 is 545, but I added 2 too many; so I
subtract 2 from 545 to get 543.”
c) For 4500 plus 1900, think, “4500 + 2000 is 6500 but I added 100 too
many; so, I subtract 100 from 6500 to get 6400.”
d) For 0.54 plus 0.29, think, “0.54 + 0.3 is 0.84 but I added 0.01 too
many; so, I subtract 0.01 from 0.84 to compensate, to get 0.83.”
Practice Items
56 + 8 = 72 + 9 = 44 + 27 =
14 + 58 = 21 + 48 = 255 + 49 =
371 + 18 = 125 + 49 = 504 + 199 =
304 + 399 = 526 + 799 = 676 + 197 =
1300 + 800 = 5400 + 2900 = 6421 + 1900 =
3450 + 4800 = 2330 + 5900 = 15 200 + 2900 =
4621 + 3800 = 2111 + 4900 = 2050 + 6800 =
30 Mental Math – Grade 6