We need units of measurement. When you say 20x15 pavers, is that inches, feet, centimeters?
120
80
ANSWER 16 x 16 inch = 1.78 sq.feet 120 / 1.78 = 67.42 so you need to have 68 pavers The plot is 144 inches wide. 144/16=9 pavers wide. The short dimension is 120 inches which would require 8 pavers with the final row of pavers cut to fit. Thus in a 9 X 8 paver grid you'd need 68 pavers, but 4 of those pavers would have to be cut in half for the final row.
120
The patio is 10x 12 = 120 sq ft or 17,280 sq in The pavers are 16x16 = 256 sq in So you need 17280/256 = 68 pavers
119.808 or about 120
135 Always get extra for breakage.
Assuming that the size refers to 24 INCHES by 24 INCHES, each paver will cover 2 ft * 2 ft = 4 sq ft So, to cover 120 sq ft will require 120/4 = 30 pavers. This also assumes that the shape that is to be covered is "well behaved" and that all offcuts can be used. In that respect, it is a mathematical answer. For real life, depending on your skill level go for 5-10% more pavers.
The area of a 16 inch x 16 inch paver is 16/9 square feet. Area to be covered = 120 sq ft So number of pavers required = 120 / (16/9) = 67.5 Thus, a minimum of 68 pavers are required. However, that assumes that the pavers fit the area well and that all the offcuts can be used - a very unlikely proposition in real life.
8 x 10 ft is 96 x 120 inches 6 x 16 = 96 and 8 x 16 = 128 so you need 6 x 8 ie 48 pavers. If you are very good with a cutter you could manage with 8 less ie 7½ x 16
120
You would need 7.5 gallons to get 120 8 ounce servings.