# Question A Day July 19 - Videos

24
87

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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1. Pradeep Singh

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. Aayush Gupta

505 is the ans.
I calculated the ans. As follows
I saw that the series is in A.P so calculated the total sum and used the basic sum formula of AP.
(46,47,…55)

3. Mohit Singh yadav

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

4. SMILE INC.

{N (n+ 1)}/2. Use 2 time. & ——-

5. Pawan Gautam

505

6. Abhishek singh

505

7. Krishnanand Shah

505

8. chirag gohel

505
series is 46 to 55
ans =(55*28)-(45*23)=505

9. Shiv Wadhwa

505 ans

10. Shivam Anand

505

11. Shivam Tiwari

505

12. manoj anand

505,from 46 to 55

13. jitu jat

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

14. Manish Gahlaut

505

15. rajnish kumar

Since the fifth row will be start from 45to 55.applying the sum formula of AP I. e n/2(a+l) we get 505 as the ans

16. DEEPAK KUMAR

505

17. Shashi Kant Chauhan

505

18. Anand Gupta

1 row 1 number
2 row 2 number

9 row 9 number total 45 numbers are used so 10th row start by 46 to 55
So sum is 505

19. ALOK GUPTA

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

20. AADITYA DHULL

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

21. MSD Motivation

505

22. chaudhry iftikhar

इफ्तिखार चौधरी जैसलमेर

23. Mayank Bhati

505

24. Sudhanshu Sekhar

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