The pie charts below show the percentage of five kinds of books sold by a bookseller between 1972 and 2012.

The given pie charts illustrate the number of books sold by sellers over a period of 40 years, from 1972 to 2012. Units are measured by percentage.

Overall

, it can clearly be seen that the portion was almost the same unless in 2012. In terms of the highest portion in 1972, it began with precisely 25 and experienced a slight decrease to just 20 and 12 in the second and third periods, respectively.

In addition

, Biography had a similar pattern which stood at 20 in the first period but after 20 years, it declined to 15 and finished almost half value. Regarding adult friction, started at one-fifth and

then

witnessed a small rose to 25. From

this

point onwards, it reached a peak of approximately 45.

Moreover

, children's friction, had an upward trend from 20 to exactly 25 by 40 years. Interestingly, different from others, travel had a fluctuating condition which started from 15 and got a small growth to 18, but dropped dramatically in the final year.