Question

One third of a number, z, added to one fifth of the same number is 3/5 . What is the number and why?

Answer 1

Let
z--------> the number

we know that
One third of a number, z, added to one fifth of the same number is 3/5 
so
the equation that represents this sentence is 
(1/3)z+(1/5)z=3/5
(5+3)z/15=3/5----------> 8z=9-------> z=9/8

therefore

the answer is the option
D) 9/8 , because the equation that represents this sentence is 1/3z+1/5z=3/5 .