<span>The ratio of all books to used books = all books ÷ used books = 15 / (15-6) = 5/3
</span>
<span> The ratio of new books to used books = new books ÷ used books = 6 / 9 = 2/3
</span>
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I hope that
helps!
</span>
Answer:
8c2 = 28
Step-by-step explanation:
You can plug this into your calculator (on a TI-84, it's MATH -> PRB -> 3) as 8 nCr 2.
Let's try to understand what the output means, though! The nCr function is based on Pascal's Triangle (see the attachment for a picture).
When we do 8 choose 2, we are basically thinking about having 8 possible values and 2 spots to fit them in, and we don't care about what order they're in. The probability of this is 8*7 / 2 = 28. Our answer makes sense!
The average change in the field position on each run is. -1 3/4
Options are not shown but…
A square has 4 equal length sides and a right angle
Or two equal length diagonals which are perpendicular
Or 4 right angled corners and two adjacent sides equal
Or perpendicular diagonals with the same midpoint
Using the last one…
Gradient of AC = (5 - 3)/(-3 - 3) = 2/-6 = -1/3
Gradient of BD = (7 - 1)/(1 - -1) = 6/2 = 3
-1/3 x 3 = -1 so AC and BD are perpendicular
Midpoint of AC = ((-3 + 3)/2 , (5 + 3)/2) = (0, 4)
Midpoint of BD = ((1 + -1)/2 , (7 + 1)/2) = (0, 4)
QED
