Thanks for your reply elmerRex, great food for thought.

Here's a few of the problems from CWP - page 32-33:

158+93+42

997+605

126-75

163-92

85x5

462x5

620/5

905/5

There are a lot of suggested worked examples, but my initial thoughts were why not pull out the calculator and be done with it?

Is the child allowed to see the problems while they work them? Or must they go by hearing only? When they are not mastered with the technique, my children find it easier to look at the problem while they figure it in their head until they gain more fluency with the technique. Only my oldest can do these problems by ear only and that is after a couple of years of regular learning and practice.

Here is how I would be coaching a child to do each of those problems mentally.

Always find tidy numbers where you can.

158+93+42 becomes **158 + 93 + 40 + 2** becomes** 160 + 40 + 93 **becomes 200 + 93 = 293

997+605 becomes **997 **+ **602 **+ **3** becomes 1000 + 602 = 1602

126-75 becomes **(100 + 26) - 75 **becomes **100-75** + 26 becomes **25 **+ 26 = (25 + 25) + 1 = 51

163-92 becomes **100 + 63 - 92 **becomes **100-92** + 63 becomes **8** + 62 + 1 becomes 70 + 1 = 71

85x5 becomes (80+5) x 5 becomes 400 + 25 = 425

462x5 becomes (400 + 60 + 2) x 5 becomes 2000 + 300 + 10 = 2310

620/5 becomes (600 + 20) / 5 becomes 120 + 4 = 124

905/5 becomes (900 + 5) / 5 becomes 180 + 1 = 181 and here, since my child wouldn't know 5*18 rote, we'd work back from 5*20 (Which they know by rote) 5*20=100, so that's too big. 5*19=100-5 or 95, so obviously 5*18=19, or 5*180=190.