Răspuns:
Ma=(7+11+36)/3
Ma=18
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Ma=(¹⁸⁾3/8+¹²⁾5/12+⁹⁾41/16+¹⁶⁾5/9)/4
Ma=(54/144+60/144+369/144+80/144)/4
Ma=(563/144)/4
Ma=563/144·1/4
Ma=563/576
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Ma=(⁵⁾7/2+²⁾4/5+¹⁰⁾5)/3
Ma=(35/10+8/10+50/10)/3
Ma=93/10·1/3
Ma=93/30=31/10
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(a+40)/2=30
a+40=30·2
a=60-40
a=20
