Sammi bought 2 dozen valentines how many valentines did sammi lave left after giving 7/8 of them to her classmates

v: l•w•h÷2.

v: 20•6•8 ÷2

v: 960÷2

v: 480

hello from mrbilldoesmath!

answer:

a(n) - a(n-1) -3

discussion:

this ones a bit interesting. given a(n) = 5 - 3n consider this:

a(n-1) = 5 - 3(n-1)

          = (5 - 3n) + 3             => but a(n) = 5 - 3n, the first term

          = a(n)   + 3                 => subtract 3 from both sides

a(n-1) -3 = a(n)  

or

a(n) - a(n-1) -3

you,

mrb