There are few printing mistakes in the book. On page number 80, in topic “multiplication”, there is a misprint and instead of writing a^1 x a^2 = a^1+2 = a^3 , a^1 + 2 is written. Also, on page number 124, in question number 9, I don’t think we can arrive at term R = 4/360 in any case (am I missing something?).

Hmmmm. It looks like you're right.
It should be 3/4 R = 60
R = 240/3
R = 80

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