Arithmetic

Question 1

To find the # of options from a given # of sources, one choice selected from each source.

Answer 1

Multiply each of the source options together.

Question 2

To find the number of arrangements in a set of elements.

Answer 2

Write out blanks for each position and write the # of elements that could go in all the blanks.

Question 3

To find the number of arrangements in a set of elements with a restriction.

Answer 3

Write out blanks for each position and write the # of elements that could go in all the blanks, accommodating for the restrictions.

Note that if the restriction involves duplicates it is easier to find the total # of possibilities and then subtract out the incorrect possibilities (map out with blanks the possible non-solutions).

Question 4

To calculate # of groups.

Answer 4

1. Draw blanks for each item.
2. Fill in blanks for each # of choices possible for that blank.
3. Divide by the factorial of the number of items (# of blanks) that were selected from the source.
4. If there are restrictions, find the total groups then subtract out the groups that would be restricted.

Question 5

harmonic mean (for speed problems)

Answer 5

n/(1/x)+(1/x)+(1/x)