 Percentage change Increase = new value - original value Percentage increase = increase / original value x 100% New value = original value x (1 + percentage increase) Decrease = original value - new value Percentage decrease = decrease / original value x 100% New value = original value x (1 - percentage decrease) Percentage change = (new value - original value) / original value x 100% Profit and Loss Profit = selling price - cost price Profit % = profit / cost price x 100% Profit = cost price x profit % Selling price = cost price x (1 + profit %) Loss = cost price - selling price Loss % = loss / cost price x 100% Loss = cost price x (1 - loss %) Discount Discount = marked price - selling price Discount % = discount / marked price x 100% Selling price = marked price x (1 - discount%) Simple interest I = PRT / 100 A = P + I = P (1 + RT / 100) Euler's formula (a convex polyhedron) F + V - E = 2 Total Surface Areas and Volumes of Prisms Total surface area of a prism = areas of the two bases + total area of all lateral faces Volume of a prism = area of base x height Angles Related to Intersecting Lines ∠s at a pt. adj. ∠s on st. line vert. opp. ∠s Angles Formed by Parallel Lines and a Transversal corr. ∠s, AB//CD alt. ∠s, AB//CD int. ∠s, AB//CD Conditions for Two Lines to be Parallel corr. ∠s equal alt. ∠s equal int. ∠s supp. Conditions for Two Triangles to be Congruent SSS SAS ASA AAS RHS Condition for Two Triangles to be Similar AAA 3 sides proportional ratio of 2 sides, inc. ∠