A book has 850 pages. The ratio of number of pages 'with illustration' to that 'without illustration' is 4 : 1. How many pages of the book have illustration?

680

with illustration  :  without illustration

           4           :           1

According to question ,

5R = 850

1R = 170

So, Number of pages with illustration = 4R

= 4 × 170

= 680