If the average of 31, x, 42, 39, 56, 78, 83 and 91 is 58.5, then what is the value of x?
Number of terms = 8
Sum of terms = $$31+x+42+39+56+78+83+91=(x+420)$$
Average = $$\frac{x+420}{8}=58.5$$
=> $$x+420=58.5\times8$$
=> $$x=468-420=48$$
=> Ans - (D)
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