sum of arithmetic sequence

[red and white kop!]

A woman started a business with a workforce of 50 people. Every two weeks the number of people in the workforce is increased by 3 people.
How many people were there in the workforce after 26 weeks (I answered 89, which is correct.)
Each member of the workforce earned $600 per week. What was the total wage bill for this 26 weeks?

I used the formula for the sum of an arithmetic sequence S=0.5n(a+l) and (for convention) 'eliminated' every other week where the wage bill remained the same to come up with S(half the wage bill) = 0.5 x 13 x (30 000 + 51 600)
So the total wage bill is 13 x 81 600 = $ 1 060 800

However the textbook gives the answer to be $ 1 341 600
Where did I go wrong?

 

[Deleted member 4993]

A woman started a business with a workforce of 50 people. Every two weeks the number of people in the workforce is increased by 3 people.
How many people were there in the workforce after 26 weeks (I answered 89, which is correct.)
Each member of the workforce earned $600 per week. What was the total wage bill for this 26 weeks?

I used the formula for the sum of an arithmetic sequence S=0.5n(a+l) and (for convention) 'eliminated' every other week where the wage bill remained the same to come up with S(half the wage bill) = 0.5 x 13 x (30 000 + 51 600)
So the total wage bill is 13 x 81 600 = $ 1 060 800

However the textbook gives the answer to be $ 1 341 600
Where did I go wrong?

As far as I can tell, your interpretation is correct.