Christian 5 Adding Round and Compensate stage 6.doc

Adding and Subtracting Strategies

Adding: Round and Compensate (When one number is near 100)

(1) 78 + 99 =  177    

    □ = 78 + 100 – 1

   = 177

We add on the tidy number 100 to get 178, but this is one too many, so the answer is 177

We can show this strategy on an empty number line:

(2) 187 + 98 =   285

□ = 187 + 100 – 2

    = 285

Use number line jumps to do these problems.

Exercise 1

What to do:

• Do the problems in your head first.

• Check you are right by writing them down.  Show them like the example above.

(1) 56 + 99 = 155       (2) 67 + 98 =165     (3) 97 + 63 = 160 (4) 38 + 98 = 136

              _ = 56 + 100 - 1                   _ = 67 + 100 - 2                 _ = 97 + 100 -  37                   _ = 38  + 100  - 2

                    = 155                                      = 165                                   = 160                               = 136

(5) 55 + 97 = 152       (6) 97 + 86 = 183    (7) 53 + 97 =140 (8)       65 + 98 = 163

              _= 55 + 100 - 3                  _ = 97 + 100 - 14                   _ = 53 + 100 - 13                    _ = 65 + 100 - 2

                        = 152                               = 183                                     = 140                                 = 163

(9) 76 + 99= 175       (10) 97 + 28 = 125

   _ = 76 + 100 - 1          _ = 97 + 100 - 72

    = 175                         = 125

Bigger numbers

  (11) 125 + 98= 223     (12) 199 + 85 = 284    (13) 198 + 73 = 271    (14)   197 + 84 = 281

          _ = 125 + 100 - 2                        _= 199 + 100 - 15              _=198 + 100 - 27                   _=197 + 100 - 16

                     =223                                           = 284                                = 271                                   = 281

  (15) 196 + 67= 263     (16) 126 + 99 = 225     (17) 234 + 96 = 340     (18) 297 + 88= 385

         _ =196 + 100 - 23                   _=126 + 100 - 1                    _=234 + 100 - 4                _= 297 + 100 - 17

                       =263                                  = 225                                      =240                                    =385

   (19)398 + 67 = 465     (20) 314 + 397 = 711    

          398 + 100 - 33       _=314 + 100 + 297  

                 = 465                         = 711.

Exercise 2 Word problems

(1) Tony Hawk gets 298 points in an Xbox game, then another 236 points the next day. How many points does he have altogether?

:534

(2) Crash Bandicoot crashes 46 times in level one and another 97 times in level two. How many crashes does he have altogether? :  40+90=130

130 + 6 + 7 = 143

(3) The artists drew 697 cartoons that got used in Shrek 2, and 259 that were not used. How many were drawn altogether? :  697 + 250 = 847 + 9= 956  

(4) Goldenhorse sold 596 disks in the first week and 234 more the next week. How many is that altogether? : 830

(5) Write two word problems of your own that could be done using this strategy.:

1.155  +  __  =344

155+200= 355 -11

          =344

2. 356 + 96= 452

300 + 90 = 390

390 + 50 + 90 = 530

6 + 6 = 12

12 + 530 + 390 = 932.