Friendly Numbers But Not
  November 4, 2019   Friendly Numbers But Not!   The following NT with preservice teachers included the following clusters:   999 +99  998 + 49  199 + 99 + 49    999 + 99 is 1098.   Me: How did you get 1098? Explain your thinking?   Katherine: I added 1 to 999 to make 1000 and took 1 from 99 to make 98.    1000+ 98 equals to 1098.    All three seemed to have the same idea.     998 + 49 is 1047   Me: How did you get 1047?  Explain your thinking.   Chase: I separated  998 to make 990 +8 and 49 to make 40 + 9.   Then I added 990 +40 which equals to 1030 and 8+9 equal 17.   1030 +17 equals 1047.   Katherine: I just did like I did before but I took 2 from 49   and added it to 998. 998+2 equals 1000. 49-2 equals 47. 1000+47=    1047.     199 +99 + 49 is 347   Katherine: I took 2 from 49 and added it to 199 and 99.   199+1 is 200 and 99+1 is 100. 200 +100 equals to 300+ 47. 347   Erika: 199 +1 is 200               99 +1 is 100    ...