An important question from ML Agarwal of Class10 for board examination. In this question we have been asked to find the sum of all two digits odd positive numbers.
ML Aggarwal
Arithmetic Progression
Chapter 9 Question 21 i
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All three-digit natural numbers which are divisible by 7 are
105,112,119,126,...,994 which are in AP with a=105,d=7,l=994
Let the number of these terms be n. Then,
an=994
a+(n−1)d=994
105+(n−1)×7=994
n=128
Now, Sn=2n(a+l)
Sn=2128(105+994)=70336.