Dear student,

From the question we get

=  35  , So

Sum of 11 observation =  35 $×$ 11  =  385

Now each observation is then changed to 15 less than 4 times the original observation.

So , we have

Sum of new 11 observation  =  [ 4 ( 1st observation ) - 15 ] + [ 4 ( 2nd observation ) - 15 ] + [ 4 ( 3rd observation ) - 15 ] + ... + [ 4 ( 11th observation ) - 15 ]

So,
Sum of new 11 observation  =  4 ( 1st observation + 2nd observation + 3rd observation + ...+ 11th observation  ) -  15 $×$ 11

Sum of new 11 observation  =  4 (Sum of 11 observation  ) - 165

Sum of new 11 observation  =  4 ( 385  ) - 165

Sum of new 11 observation  =  1540 - 165

Sum of new 11 observation  =  1375

So

New Mean = $\frac{1375}{11}$ =  125  ( Ans )
Regards

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