In lesson 14, multiplying near base 100(other bases also),the vertcally and crosswise method is really a faster way to get the answer as compared to the conventional method.And the added advantage is that it works for other bases (ex,200,200 etc) also.
The three proofs(Arithmetic,Geometric and Algebraic)are well explained to answer why the method(for multiplying numbers near base) works.
Extension of base multiplication method ,use of “Proportionately” in solving other multiplication problems is helpful.Also,it saves lot of time in doing the calculations.
Table patten,Sequence Pattern are intresting topics.Really enjoyed representing the sequence on the 9-point circle.I drew the table pattern(for 7 times table).
The use of “reversing” is explained in a simple manner in “Thinking of a number”.
Also, the use of equations in finding the “unknown number” is explained in a good way, especially when we are doing it mentally .
Had a great learning.