Question

In a certain sequence of numbers, each term after the first is found by doubling and then adding $3$ to the previous term. If the seventh term of the sequence is $125$, what is the first term?

Answer 1

5

Explanation:

(see attached)

Answer 2

Given
`a_7=125` you can find a_6:


`a_6= (125-3)/(2) =61`

`a_5= (61-3)/(2) =29 \\ a_4= (29-3)/(2)=13 \\ a_3= (13-3)/(2) =5 \\ a_2= (5-3)/(2) =1 \\ a_1= (1-3)/(2)=-1`
Answer: -1