Answer
The new mean:
$M=18$
Work Step by Step
$M=\frac{∑X}{N}$
There are 7 scores whose mean is $16$:
$16=\frac{X_1+X_2+X_3+X_4+X_5+X_6+X_7}{7}$
$X_1+X_2+X_3+X_4+X_5+X_6+X_7=16\times7=112$
Now, let's change one of the scores from $6$ to $20$. Since the position of this score in the sum above makes no difference, let's name this score as $X_7$
Before:
$X_1+X_2+X_3+X_4+X_5+X_6+X_7=112$
$X_1+X_2+X_3+X_4+X_5+X_6+6=112$
$X_1+X_2+X_3+X_4+X_5+X_6=106$
After:
$X_1+X_2+X_3+X_4+X_5+X_6+X_7=106+20=126$
Find the new mean:
$M=\frac{∑X}{N}=\frac{X_1+X_2+X_3+X_4+X_5+X_6+X_7}{7}=\frac{126}{7}=18$
