Question

Two thirds of a number plus 5 is greater than 17

Answer 1

In expression form this is: 
2/3n + 5 > 17 
Hope this helps!

Answer 2

What the sentence is trying to say, is 2/3 of x+5>17. If you want the number, you're going to need to plug in a number into the variable. Let's say 5 for an example.  2/3 of 5 is 3.33,+5 is 8.33>17. That statement is not true, so we go onto a bigger number, like 14. 2/3 of 14 is 9.33+5 is 14.33, also not true. 2/3 of 18=12+5= 17, still not true. 2/3 of 24 is 18+5 is 23>17, which is true.
hope it helped :P