Mental Computation – Addition

Your goal for learning mental computation is to have a wide variety of mental methods, use opportunities where each method can be employed, and   use mental methods regularly to improve your skills.

• Front End Addition (Review)

This strategy involves adding the highest place values and then adding

the sums of the next place value(s).

  

Examples

a) For 37 + 26, think: “30 and 20 is 50 and 7 and 6 is 13; 50 plus 13 is 63.”

b) For 450 + 380, think, “400 and 300 is 700, 50 and 80 is 130; 700 plus

130 is 830.”

c) For 3300 + 2800, think, “3000 and 2000 is 5000, 300 and 800 is

1100; 500 plus 1100 is 6100.”

d) For 1.4 + 2.5, think, “One plus two is 3, and 4 tenths plus 5 tenths is

9 tenths, so the answer is 3 and 9 tenths. 3.9

Practice Items

45 + 38 =                 34 + 18 =                                  53 + 29 =

340 + 220 =             470 + 360 =                              607 + 304 =

3500 + 2300 =         5400 + 3 400 =                         6800 + 2100 =

4.6 + 3.2 =               5.4 + 3.7 =                                1.85 + 2.25 =

3.3 + 2.4 =                6.6 + 2.5 =                                0.36 + 0.43 =

Some sums on multiplication and division of Decimals

1.     Multiply    2.45   X   3.2                       2. Multiply  2.08  X 3.9

3.  Multiply   2.654  X  5.05                       4 Divide. 3.09 ÷  3.2

5. Divide     6.789  by 4.2