Xiao Ming was reading a storybook. He had already read 40% of the book, and there were still 90 pages left. How many pages does this book have?

This book has a total of $90+ 40%$ $×$pages. Substituting 40% into the above formula: $90+04×$ $×$pages = $90+04×$ $×$ (100-90) = $90+04×$ $× $10 = $90+04×$ $× $100 = $90+40=130$pages Therefore, the book had a total of 130 pages.

This book had a total of 180 + 5/6 = 195 pages.

Xiao Ming had already read two-fifths of a 200-page storybook, which was 10 pages more. 200 pages × 2/5 + 10 pages = 40 pages The remaining pages were: 200 - 40 pages = 160 pages Therefore, Little Ming still had 160 pages left.

Let's say this storybook has a total of $x$pages. According to the topic, 30 pages per day meant $30/div2 = 15$per hour. Zhang Ming read $15$pages per hour in $3$days so he read $3/30 = 90$pages in total. The remaining pages are $8/5 of the book, so there are: $$ 90 - \frac{8}{5} = \frac{16}{5} $$ Because the question requires the number of pages in the book, you need to multiply this result by $x$pages to get: $$ x \times \frac{16}{5} = \frac{16}{5} \times x = 96 $$ Solve this equation to get $x = 56$. So this story book had a total of $56$pages.

Xiao Ming read a total of $4/15 = 60$pages in 4 days. The remaining pages are $2/5$of the book, so the book has a total of $2/5/60 = 48$. Thus, the book had a total of 48 pages.

Assuming that this storybook had $x$pages, then the number of pages Little Light read every day was $15/div4 = 375$pages. Little Light had already read $4$for days, so the remaining pages were $x - 4/375 = x - 1125$. Because the number of pages Little Light reads every day is fixed, the number of pages can be expressed as: $$x - 4 \times 375 = 375 \times 4 - 1125$$ The above formula was simplified to: $$x = 48$$ Therefore, there were still $48 - 1125 = 3675 pages of this storybook that he had not read.

Xiao Ming had already read 80 pages, so the number of pages he had read accounted for 2/3 of the total number of pages. The remaining pages were 150 - 80 = 70 pages. Therefore, the remaining pages accounted for 1/3 of the total number of pages.

There were 170 pages in a book. He had already read 90 pages, so there were still 80 pages left.

Xiao Ming had already read two-fifths of a 150-page storybook, so he had already read 150 × 2/5 = 60 pages. Therefore, there were still 150 - 60 = 90 pages left in the storybook.

Lil 'Fatty had already read half of the book. Three pages were missing, which meant 1/2 - 1/2 + 3 = 2/3 pages. Therefore, Lil 'Fatty had already read 2/3 of the pages and there were still 90 pages left. This meant that the book had a total of 90/2/3 = 90/3 = 300 pages. Therefore, the book had a total of 300 pages.