Answer:
<h2>A. -2</h2>
Step-by-step explanation:
![\det\left[\begin{array}{ccc}a&b\\c&d\end{array}\right] =ad-bc\\\\\det\left[\begin{array}{ccc}3&-5\\1&1\end{array}\right] =(3)(1)+(-5)(1)=3-5=-2](https://tex.z-dn.net/?f=%5Cdet%5Cleft%5B%5Cbegin%7Barray%7D%7Bccc%7Da%26b%5C%5Cc%26d%5Cend%7Barray%7D%5Cright%5D%20%3Dad-bc%5C%5C%5C%5C%5Cdet%5Cleft%5B%5Cbegin%7Barray%7D%7Bccc%7D3%26-5%5C%5C1%261%5Cend%7Barray%7D%5Cright%5D%20%3D%283%29%281%29%2B%28-5%29%281%29%3D3-5%3D-2)
77(7) = 539, the total points of all her tests
539 - 18 + 81 = correct total points = 602
602/7 = 86 which is the new average
It would be: 567/18 = 31.5
So, she needs atleast 32 shelves....
So this is basically a ratio and the form I use to solve these is
Is. = %
Of. 100
So we're looking for 5% of the 350,000 which will be x
X. = 5
350000. 100
Cross multiply
100x=1750000
Divide by 100
X=17500