The number of cars in first month = 11
Number of cars in second month = 11 + 9 =20
Number of cars in third month = 20 + 9 = 29
If we observe, the number of cars form an Arithmetic sequence with first term as 11 and common difference 7. We are to find the total cars received till the end of 7th term in the shop i.e. we are to find the sum of first 7 terms of the sequence.
So, using the formula of sum Arithmetic series we can write:
Cars received in 7th months = [tex] \frac{7}{2}(2(11)+(7-1)(9)) = 266 [/tex] cars
Thus, 266 cars were received at the end of 7th month at Jonathan's auto repair shop.
