In a classroom, a Maths teacher is asking questions to her students. She first asked the class to see if they could find the sum of the first 50 odd numbers. As everyone settled down to their addition, Mark ran to her and said, The sum is 2,500. The teacher was surprised so to test if Mark actually calculated the sum or was guessing she gave him the task of finding the sum of the first 75 odd numbers.Within 20 seconds, Mark was back with the correct answer. How does Mark find the sum so quickly and what is the answer

1

Answers

2016-02-17T06:10:30+05:30
Mark could calculate the sum so fastly because he was using AP and its Sn formula to find the answer.

Given :- AP :- 1, 3, 5, .......
here, a = 1, d = 2, n= 75
Sn = n/2[2a+(n-1)d]
Sn = 75/2 [ 2*1 (75-1)*2]
Sn = 75/2 [ 2 (70*2) ]
Sn = 75/2 [ 2*140 ]
Sn = 75/2 [ 280 ] 
Sn = 75*140
∴Sn = 10500

Thank you.....!!!!
Mark as brainliest of helpful..
Yours, Jahnavi.
0