On Monday, October 5, 2015 at 10:55:33 PM UTC-4, wrote:
to take the slab. He said he had used about 5 bags of concrete but I'd feel better if i could see that in print...


If you really need 2.2 cubic yards like your diagram says, you need about ninety 80 pound bags, not the 5 you mentioned. One bag is about 2/3 of a cubic foot, not yard; a yard has 27 cubic feet.

You'd be dumb to mix it. Delivered it's only about $100 - $150 a yard, if you can get a concrete truck to deliver a small quantity.