Subtraction & Addition

Subtraction is often faster in two steps instead of one.

 Example: 427-38=(427-27)-(38-27)=400-11=389

                GOLDEN RULE             "First remove what's easy, next whatever remains".
                                                         Example :    2931 -1243    =2800-1200+131 -(31  +12)
                                                                        =1600 +100-12  = 1600   +88  =1688

                                                         Example:      4878 -  496    =  4878+4 -(496 +4)
                                                                             4882 -500     =  4382

                                                         Example:   1048-189=1048+11 -( 189+11.)
                                                                                          = 1059  -200  =859

                                                         Example:   1893-1245  =1893+7-( 1245+7)
                                                                          1900 -1252 =648

Addition.

Addition is often faster in two steps instead of one.

Example: 495+38=(495+5)(38-5)=500+33=5

                   GOLDEN RULE             "First add  what's easy, next whatever remains

                                                             Example:  1256 +289   = 1300 +289-44
                                                                                                 =1300+245=1545

Example:   1893+1245  =3193+7+( 45-7)
                                         3200 +38=3238

                                                             Sometime it is easy and quite fast if we start with higher digit
                                                             Example: 952 +687 =1500+52+87
                                                                                              =1600+52-13
                                                                                              =1600+39
                                                                                               =1639