what is the solution of this question?

Question

the mean and standard deviation of 100 observationss were worked out as 40 and 5 respectively. but by mistake a value 50 was taken in place of 40 for one observation. recalculate the correct mean and standard deviation.

Answer 1

solution of this question -in trapezium ABCD,ABparllel DC and L is midpoint of BC . through   L, a linePQprallelAD has been drawn which meets AB in P and DC produced in Q. Prove that (ABCD)=ar(APQD)