Kevin will be taking six classes next semester (Algebra, World History, Psychology, Political Science, Chemistry, and Art Theory) and would like to know how many different ways he can order his class schedule given that his university offers six time slots for classes each day. Assuming there are no constraints and each class can be taken in any time slot, how many different ways can Kevin order his classes?

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Explanation:

We have 6 slots to fill A,B,C,D,E,F

There are 6 choices for choice A, then 5 choices for slot B, 4 for C, and so on until we reach one choice for slot F. Count down by 1 each time a slot is filled.

Multiply out those values to get: 6*5*4*3*2*1 = 720

For more information, check out the concept of factorials.

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Another approach is to use the nPr permutation formula which is

where in this case n = 6 and r = 6.

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