Wanted solution of Q 17 Sonia has 55 blocks She decides to to stack up all the blocks - Maths - Sequences and Series

Question

Wanted solution of
Q 17 Sonia has 55 blocks She decides to to stack up all the blocks
so that each row has one less block than below She wants to end up
with just 1 block on top How many should she put in the bottom row?

Lovina Kansal · Accepted Answer

Dear student
Clearly, Here common difference,d=-1and last term,l=1Also, Sn=n2a+l⇒55=n2(a+1)⇒110=n(a+1)    
(1)and,an=a+(n-1)d⇒1=a+(n-1)(-1)⇒1=a-n+1⇒a=nPut the value of n=a in (1), we get110=n(n+1)⇒110=n2+n⇒n2+n-110=0⇒n2+11n-10n-110=0⇒n(n+11)-10(n+11)=0⇒(n+11)(n-10)=0⇒n+11=0 or n-10=0⇒n=-11  (rejected) or n=10So, Sonia should put 10 blocks in the bottom row
Regards

Wanted solution of Q.17. Sonia has 55 blocks. She decides to to stack up all the blocks so that each row has one less block than below. She wants to end up with just 1 block on top. How many should she put in the bottom row?

Wanted solution of
Q.17. Sonia has 55 blocks. She decides to to stack up all the blocks so that each row has one less block than below. She wants to end up with just 1 block on top. How many should she put in the bottom row?