Here is a number sense trick to help you calculate subtraction using mental math.

We want to find the difference of 100 – 76. Using our number sense, we turn to “friendly numbers” to calculate how far apart are 76 and 100.

Starting at 76, we can first find how far apart are 76 and 80 (the nearest multiple of 10) and get 4.

Here is a number sense trick to help you calculate addition using mental math.

We want to find the sum of 9 + 8 + 7. Using our number sense, we turn to “friendly numbers” such as 10 or multiples of 10, to help make this math easier to work with.

The word quarter means “4 parts the same,” “four equal parts”.

To find a quarter of any amount, cut the whole into “4 parts the same” and take any one part. The trick to doing this easily is to “cut it in half and then cut the half in half and take any piece.” A quarter also means “half-of-a-half.”

To find one quarter of 8 we cut the whole of 8 circles into “4 parts the same” by cutting the whole in half, and then the half in half.