I'm a neophyte here trying to learn using "Practical Electronics for Inventors, 4th Edition" (which received almost a 5 star review with over 500 reviews on Amazon). The preface of the book states "little to no experience" in electronics needed to understand the concepts in the book.
Alas, I'm struggling on the Theory chapter less than 20 pages in. When asked to solve the below questions. The book presents a few sentences which are relevant, but not enough for me to understand and solve the questions posed after.
The book states (and I believe I understand) the idea that Voltage is the measurement between two points usually provided by an absolute scale which is often set at 0 on the negative terminal (ground reference). This is at least true for the DC circuits discussed. The illustrations show (with enough clarity) an example of the V between the positive and negative of a single 1.5V battery, two batteries in series (3V), and finally an example of a split supply with a common return - a ground reference between the positive and negative leads of the two batteries. While I don't understand all the ramifications of this yet, I understand the basic explanation.
Several pages later the following questions are posed, along with the answers which I am having a lot of trouble following. I understand they are trying to show some examples that don't have a ground reference and/or that the ground reference is either at the positive or negative end, but lack of a walkthrough of prior examples is leaving me stumped. Furthermore there is a possibility based on this question that the book may be incorrect - which would be very disappointing as it is hard enough for me as it is.
Any insight into how to help me interpret these answers or clarification on the basic theory being illustrated below is appreciated: