Question A Day July 19 - Videos

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What would be sum of 10th row of the below given series
1
2 3
4 5 6
7 8 9 10
11 12 13 14 15
………………………………..

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24 COMMENTS

  1. This is a pyramid of numbers in which every row includes that much numbers as the rows place. …So either start from 1,2,4,7….find the first no. Of tenth row and add those ten no or Start from from 1,3,6,10….find the last no….then reduce to ten no. Before that no ….Nd add it ….therefore ll be 101×5=505

  2. 505…. It's based on the AP… If we notice the left side it is a series and we can obtain Ap by subtracting the same no. Just increase there place value by 1 i.e 2-1,4-2,7-4….=1,2,3….
    So 1+(1+2+3+…..9)=46(our first no. Of 10th row
    We have our 10th row 46,47,48…….55 =10*(46+55)/2=505

  3. Sir this question solved as 46 to 55 no tak sum so S=n(a+l)/2 …. n is total no is 10 and a is starting no 46 . l is last no 55 then S=10(46+55)/2=505 ans

  4. 505
    because in 6 th serease six no added AND seventh serease 7 nobers added and so on similarly in 10th serease 10 no added that is 46 to 55 and use ap n/2{a+l}=505 ans

  5. For 2nd last term is 3
    (2*3/2)==3
    For third row last term is 6
    (3*4/2)==6
    Fourth row last term is 10
    (4*5/2)==10
    Similarly last term of 9th row will be (9*10/2)==45
    First term is 46 and this row has 10 terms
    (n/2)(a+(n-1)*1)==(a=46,n=10)
    505

  6. We can work on the middle term…1 in 1st row, 5 in 3rd row, 13 in 5th row ,25 in 7th row and 41 in the 9th row..or we have (41+9)=50 and (41+10)=51 as the 2 middle term in the 10th row..so (50+51)/2=50.5*10=505 is the ans

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