Answer:
<u><em>120.</em></u>
Step-by-step explanation:
<em>Let the common difference be d. Then these equations are true,
</em>
<em>so add all the left sides and all the right sides:
</em>
<em>
</em>
<em> y = 30-d
</em>
<em> x = 30-2d
</em>
<em> z = 30+d
</em>
<em> f = 30+2d
</em>
<em>-------------------------
</em>
<em> y+x+z+f = 120
</em>
<em>
</em>
<em>Notice that there are lots of different possibilities for x,y,z,f.
</em>
<em>
</em>
<em>For example the arithmetic sequence could be </em>
<em>
</em>
<em>10 20 30 40 50, which have sum 120 with d=10, or
</em>
<em>
</em>
<em>20 25 30 35 40, which also have sum 120 with d=5, or </em>
<em>
</em>
<em>54 42 30 18 6, which also have sum 120 with d=-12, or any of
</em>
<em>an infinite number of possible arithmetic sequences. But the
</em>
<em>sum will always be 120.</em>
