Cross multiply
10 x 9 = 90
3 x k = 3k
make an equality
90 = 3k
divide both sides by 3
90/3 = k
simplify
30 = k
120 cupcakes
Even # rows
Odd # columns
12: 1, 2,3,4,6, 12 (integers?)
I see only one arrangement with odd column & even rows
3 columns, 40 rows
That's mainly because 120 is an even number.
one+four+three=eight pens.
Two pens are selected without replacement.
Need probability of selecting two black pens.
Probability of selecting first black pen is four out of eight, 4/8
Probability of selecting second black pen is three remaining black pens out of the remaining 7 pens = 3/7
Probability of both events happening is the product of the two probabilities, according to the multiplication rule.
Therefore probability of selecting two black pens out of the initial eight pens
=(4/8)(3/7)=3/14=0.2143 (to the ten-thousandth).
Rounding to the hundredth will give you the required answer.
I belive that the answer is C