Question

15. The average length of 20 bricks is 360 cm. When
another brick is added, the average length becomes
355 cm. Find the length of the twenty-first brick.
(1) 250 cm
(2) 253 cm
(3) 255 cm
(4) None of these
24.​

Answer 1

Answer:

option 3 255cm

Step-by-step explanation:

     given that the average of 20 bricks length=360

      average=sum of observations/no of observations

     360=sum of observations/20

    sum of observations=360x20

                                      =7200cm

      the average of 21 bricks=355

       355=sum of observations/number of observations

          sum of observations =355x21

                                             = 7455cm                                                                                    the length of 21st brick =sum of observations of 21 bricks-sum of bricks of 20bricks

            the length of 21st brick=7455-7200

               the length of 21st brick is 255cm