Let the first term of A.P. be a, and d be the common difference
a+(n-1)d - a = 10.5
(n-1)d=10.5 ---------------> 1
sum of odd terms + sum of even terms = sum of the terms in A.P.
n(2a+10.5)=108 -------------> 2
Consider the series formed by all the odd terms,
first term would be a, last term is a+(n-2)d
(the no of terms in A.P. is given to be even)
n/2 (a+a+(n-2)d)/2=24 ------------> 3
You have 3 eq, 3 unknowns, solve them
n/2 (a+a+(n-2)d)/2=24
n(2a+10.5)=108
(n-1)d=10.5
You get a=1.5, d=1.5, n=8
a+(n-1)d - a = 10.5
(n-1)d=10.5 ---------------> 1
sum of odd terms + sum of even terms = sum of the terms in A.P.
n(2a+10.5)=108 -------------> 2
Consider the series formed by all the odd terms,
first term would be a, last term is a+(n-2)d
(the no of terms in A.P. is given to be even)
n/2 (a+a+(n-2)d)/2=24 ------------> 3
You have 3 eq, 3 unknowns, solve them
n/2 (a+a+(n-2)d)/2=24
n(2a+10.5)=108
(n-1)d=10.5
You get a=1.5, d=1.5, n=8