Question

What will be the sum of all 2-digit even numbers?

Answer 1

Answer:

2420.

Explanation:

12 ,14 ,16 ,.......,98. are two digit even numbers .

this is in AP .

t1 = 12 , t2 = 14 , t3 = 16 ,.........tn = 98.

tn = a+ (n- 1 ) × d.

98 = 12 + (n-1) ×2.

98 - 12 = (n-1) 2.

86= ( n-1) 2.

86÷2= n-1.

43 +1 = n

n = 44.

now I have find sum of all 2- digit even number.

Sn = n/2 [t1 + tn].

= 44\2 [12+98].

=22 ×110.

Sn =2420.

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