Ken has read 1/3 of his book what fraction of his book is left to read?

2/3

Step-by-step explanation:

fraction of book already read = 1/3

fraction which represents whole book = 1 = 3/3

fraction of remaining book = fraction of whole book - fraction of book already read

= 1 - 1/3

= 3/3 - 1/3

= (3-1) / 3

= 2/3