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(#M40030613) TECH MAHINDRA Numerical Ability question Keep an EYE

what is the sum of the first 20 odd natural numbers

Asked In Tech Mahindra Kalva Paramesh (11 years ago)

Solved RAKESH Read Solution (9)

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RAKESH  (11 years ago)

sum of first n odd natural nuber is = n^2
so sum of the first 20 odd natural numbers=(20)^2=400
ans 400

Is this solution Helpfull? Yes (27) | No (6)  

Mahesh  (11 years ago)

Sum of first two odd numbers is 4, which is 2 square
Sum of first three odd numbers is 9, which is 3 square
So, sum of first 20 odd numbers is 20 square, which is 400

Answer is 400

Is this solution Helpfull? Yes (16) | No (1)  

VIVEK KUMAR BARANWAL  (11 years ago)

SERIES IS IN AP.
1 3 5 7 . . . . . . .
20TH TERM(L)=A+(N-1)*D=1+(20-1)*2=39
SUM OF 20 TERM=20/2(A+L)=10*(1+39)=400

Is this solution Helpfull? Yes (12) | No   

s b p  (11 years ago)

4*(1+3+5+7+9) + (10*5) + (20*5) + (30*5) = 400

Is this solution Helpfull? Yes (4) | No (1)  

DHIRENDRA   (11 years ago)

firt odd natural number is = 1
second odd natural no is = 2+1=3
third odd natural no is = 3+2=5
four odd natural no is =4+3=7
fifth odd natural no is = 5+4=9
.
.
.
20 odd natural no is = 20+19=39

here firt term is = 1
comman diffrence is =2
no to terms= 20;
with the help of arithmatic sum
sum of n no=2*a+(n-1)*d
or
a+l;
where l =last term
putting the value
sum of 20 natural no is=1+39=40
or
2*1+(20-1)2
2+19*2
2+38=40 answer

Is this solution Helpfull? Yes (3) | No (21)  

Meghana kv  (11 years ago)

1,3,5,7......19=10 numbers
n(1st num+last num)/2=10(1+19)/2=5*20=100

Is this solution Helpfull? Yes (2) | No (1)  

tousif ahammad  (10 years ago)

total no n=20
sum=n/2 [1st turm + (n-1)d] d=difference
=20/2 [1+(20-1)2]
=400

Is this solution Helpfull? Yes (1) | No   

RAKESH NAYAK  (10 years ago)

No need to do long method...simply in 1 line ans can be found.....

here n=20, so sum of odd no=(n^2)....so ans is 400.

Is this solution Helpfull? Yes (1) | No   

meenakshi  (9 years ago)

here no. of terms =20
and use sum of A.P i.e
sum=n/2[2a+(n-1)*d]
here a=1 and d=2
so 400 will be the answer

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