Question

1. Find the sum of all odd numbers of four digits which are divisible by 9.
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Answer 1

Answer:

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Step-by-step explanation:

list of odd numbers divisible by 9 :

1017 , 1035, 1053,.......9999

clearly , this forms of A.P in which first term , a1 = 1017

& common difference, d = 18

an = 9999

an = a1 + (n-1)d

=> 9999 = 1017 + (n-1)18

=> 9999-1027 = (n-1)18

=> 8982/18 = (n-1)

=> 499 = n-1

=> n = 500

now , we know that ;

Sn = n/2 [a1+ an]

=> 500/2 [ 1017 + 9999 ]

=> 250 × 11016

=> 2,754,000

therefore , the sum of all odd numbers of four digits which are divisible by 9 is 2,754,000.

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