A chemistry book comprises of two sections: organic and non-organic in the ratio 2:8. How much of each type of content will be needed to make a book of 400
pages?

Given parameters:

Ratio of organic to non-organic  = 2:8

Total number of pages in the book = 400

Unknown:

Number of pages of organic = ?

Number of pages of non-organic = ?

Ratios establishes the proportion of parts in a whole.

We can find the whole from the part and likewise the part from the whole if we know the ratio;

To solve this problem;

Sum up the ratio ; 2 + 8  = 10

Number of pages of organic =   = 80pages

Number of pages of non-organic =   = 320pages

We need 80 pages of organic and 320 non- organic pages to make up the chemistry book.