Let x - 53651 = 9999 33994 be the answer. Then x = 9999 + 53651 = 63650 ——- 53651. The first 45 natural numbers add up to:
A. 1035
B. 1280
C. 2070
D. 2140
Answer:A
Let x - 53651 = 9999 33994 be the answer. Then x = 9999 + 53651 = 63650 ——- 53651. The first 45 natural numbers add up to:
A. 1035 B. 1280 C. 2070 D. 2140
Explanation: Sn equals (1 + 2 + 3 +... + 45). This is an A.P. with the following values: a = 1, d = 1, and n = 45.45/2 x [2 x 1 + (45 - 1) x 1] = 45/2 x 46 = Sn = n/2 [2a + (n - 1)d] = 45/2 x [2 x 1 + (45 - 1) x 1] = 45/2 x 46 = (45 x 23)= 45 x (20 + 3) =45 x 20 + 45 x 3 = 45 x 20 + 45 x 3= 900 + 135 + 135 + 135 + 135 + 135 +Equals 1035.Method of Shorcut:Sn = n(n + 1)/2 = 45(45 + 1)/2 = 1035