Picture puzzles are an excellent way to introduce the part – part – whole aspect of Singapore Maths, missing digits e.e. 145 + __ = 193, pre-algebra thinking and can be used to develop logical thinking with halving and subtraction.
The numbers were chosen to be used in K3 4 i.e. halving 3 digit numbers (e.g. 176) and borrowing when subtracting 3 digit – 2 digit (e.g. 263 – 87). However, if they not aren’t used to these types of visual problems, they can be used much later to introduce algebra.
I recommend using the halving diamond for the first sheet (as the start of most) and the column method to subtract and borrow.
There are three pages of scales picture puzzles.