Find the sum 1 - 0.99 + 0.99^2 - 0.99^3 + ... - 0.99^79

International calls require the use of a country code. many country codes a 3-digit numbers. country codes do not begin with a 0 or 1. there are no restrictions on the second and third digits. how many different 3-digit country codes are possible?

Can someone me with the property questions for 12 13 and 14 plz

Triangles abc and dfg are given. find the lengths of all other sides of these triangles if: b ∠a≅∠d, ab·dg=ac·df, ac=7 cm, bc=15 cm, fg=20 cm, and df-ab=3 cm.