30b + 100u = 900
5b + 25u = 200....multiply by -6
------------------
30b + 100u = 900
-30b - 150u = - 1200 (result of multiplying by -6)
------------------add
-50u = - 300
u = 6 <== upgrated phones sold
30b + 100u = 900
30b + 100(6) = 900
30b + 600 = 900
30b = 900 - 600
30b = 300
b = 10 <== basic phones sold
10.5, 11, 11.5, 12, 12.5...this is an arithmetic sequence with a common difference of 0.5
an = a1 + (n - 1) * d
n = term to find = 23
a1 = first term = 10.5
d = common difference = 0.5
sub and solve
a(23) = 10.5 + (23 - 1) * 0.5
a(23) = 10.5 + 22 * 0.5
a(23) = 10.5 + 11
a(23) = 21.5 <===
Answer:
let no.be x
its half= x/2
its one third= x/3
its one sixth=x/6
atq.....avg of x= x/2+x/3+x/6//3=6x/6//3=x/3
now...x/3+6=x...as the no.is 6 more than its avg
x= 9
