maths Maths Puzzle

Ms. Arroyo asked the class to see if they could find the sum of the first 50 odd numbers. As everyone settled down to their addition, Terry ran to her and said, "The sum is 2,500." Ms. Arroyo thought, "Lucky guess," and gave him the task of finding the sum of the first 75 odd numbers. Within 20 seconds, Terry was back with the correct answer of 5,625.

How does Terry find the sum so quickly?

Read Solution (Total 3)

she squared the no.but the answer is wrong
11 years agoHelpfull: Yes(1) No(0)

first odd no=1
75 th odd no would be 2*74+1=149
(nth odd term is=2*(n-1)+1)
sum=n/2(a+l);
n= no of terms
a=1st term
l=last term
therefore
sum=75/2*(149+1)=5625
11 years agoHelpfull: Yes(0) No(0)
first series is 1,3,5.....99
so sum =(a+l)n/2
so sum= (1+99)*50/2=2500
second =1,3,...149
sum=(1+149)*75/2
=75*75
=5625
11 years agoHelpfull: Yes(0) No(0)

maths Other Question

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