Destiny read 1/4of a book on the day she received it .the next day , read 5/8of the book . on the third day , she finished reading the book what decimal represents the fraction or the book destiny read on the third day

So what you want to do first is find the total amount of book she had read in the first and second days combined. 

So you can just add 1/4 and 5/8 together. To do this, first change their denominators to be equal.

1/4 = 2/8

Then you can just add.

2/8 + 5/8 = 7/8

So Destiny read 7/8 of the book in the first and second days combined. 

Since here we are representing the whole book as 1, just subtract the amount she has already read from the whole book.

1 - 7/8 = 1/8

So destiny read 1/8 of the book on the third day.