Let X be the random variable representing the number
of coins that Matt set aside after three flips.

We have to run n from 0 to 100 and m from 0 to (100-n),
Find the binomial law, then compute the mean like this:

Hope this gives a hint.
Answer: QS=68 units
Step-by-step explanation:
<em>RT=RS+ST</em>
<em>8x-43=2x-4+4x-1</em>
<em>8x-43=6x-5</em>
<em>8x-43-6x=6x-5-6x</em>
<em>2x-43=-5</em>
<em>2x-43+43=-5+43</em>
<em>2x=38</em>
<em>Divide both parts of the equation by 2:</em>
<em>x=19</em>
<em>QS=RS+RQ</em>
<em>As, RS=RQ</em>
<em>QS=2RS</em>
<em>QS=(2)((2)(19)-4))</em>
<em>QS=(2)(38-4)</em>
<em>QS=(2)(34)</em>
<em>QS=68</em>