Think about it like a bottle filled 1/3 of the way with each nutrient. The one with the 0 in nitrogen will dilute the npk ratio by 1/3 So nitrogen wont be 9. You could add the other 2 together and minus 33% off the weight of the mix an get your total but that's only if one has no Nitrogen at all..... if it has any you'll have to make adjustments to your math.

each number is the % by weight So one pound of 5-0-0 contains 5% nitrogen.

10 table spoons of 1-1-1 is the same as 1 table spoon of 10-10-10.