Answer:
after 6 weeks
Step-by-step explanation:
Sid and Tim starts saving each week.
Sid starts his savings with initial amount of £13.00
Tim starts his saving with initial amount of £00.00
Each week from now Sid will save = £3.50
Tim will save each week = £3.00
Let's assume after 'x' weeks the amount of Sid would be = £ (13 + 3.50x)
and the amount of Tim's saving after x weeks = £ (3x)
The ratio of their savings in x weeks would be = 17 : 9
Now the expression we get,
(13 + 3.50x) : (3x) = 17 : 9

9(13 + 3.50x) = 17(3x)
117 + 31.5x = 51x
117 = 51x - 31.5x
117 = 19.5x

x = 6
After 6 weeks the savings of Tim and Sid would be in the ratio of 17 : 9.