Question

Find sum of odd numbers between 10and 50

Answer 1

Answer:

600.

Step-by-step explanation:

From the properties of AP :

        Sum of first n terms = ( n / 2 ){ a + l }

        nth term = a + ( n - 1 )d

Here,

        first term = first odd number after 10 = 11

        last term = last odd number before 50 = 49

        Conse. terms increase by 2 = common difference = 2

⇒ 49 = 11 + ( n - 1 )2

⇒ 49 - 11 = ( n - 1 )2

⇒ 38 = ( n - 1 )2

⇒ 38 / 2 = n - 1

⇒ 19 = n - 1

⇒ 19 + 1 = n

⇒ 20 = n

            Hence,

      Sum of odd no. = ( 20 / 2 )( 11 + 49 )

                      ⇒ 10( 60 )

                      ⇒ 600

Answer 2

Answer:

600

Step-by-step explanation:

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