Question 1192834
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<pre>

If, in accordance with the common sense, s5 is the sum of 5 terms and s4 is the sum of 4 terms, 

while u5 is the 5-th term, then


    u5 = s5 - s4.
</pre>

Solved.


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It is a very bad style to present a Math problem without explanation/definition what the terms are.


Only a person, whose Math education was reading puzzles, may allow to write Math problems in this way.