Question

200 logs are stacked in the following manner : 20 logs in the bottom row ,19
in the next row, 18 in the row next to it and so on .In how many rows the 200 logs are placed and how many are in the top row ?

Answer 1

Answer:

It is an AP such that a=20 & d=−1

Sn =200

⇒200= n/2 [2(20)+(n−1)(−1)]

⇒400=n[40+1−n]

⇒n² −41n+400=0

⇒n² −25n−16n+400=0

⇒(n−25)(n−16)=0

So n=16 or n=25

T16 =a+15d=20−15=5

T25 =a+24d=20−24=−4

Since T25 is not possible.

∴ n=16 & 5 logs are placed in the top row.

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