Today, the mailman sorted 57 letters during his first hour of work, 69 letters during his second hour, 81 letters during his third hour, and 105 letters during his fifth hour. based on the trend, how many letters did the mailman sort during his fourth hour of work?

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

ghjmutmum

step-by-step explanation: