Calculators are a mess sometimes. Like, in this case, if on the very first day the student was doing the problem and encountered the fraction operation and went for a 'I will try again' than 'Where is the damn calculator'- he would have been a success in it today.
I don't know about how books in your country are designed. But, here we have books which repeat stuff, though adding a little to it, in alternate classes. Like, if in class 8 I learnt about various types of cells and how they function, I would learn about electricity in detail-with concept of resistance, voltage, power and all. If I learnt about how lens and mirrors work, just the basics; I would learn the mirror formula and lens formula in 10 and in 12 I would be deriving them all.
The problem might be in the book designing part.