Jethalal started with 49 TV sets and added five more every week until he had…

Concept: When a quantity grows by a fixed amount every period (here, a fixed weekly addition), the number of periods needed to go from a starting value to a target value is found by dividing the total increase by the fixed per-period rate: number of periods = (final value - initial value) / rate per period.

1. Identify the initial and final quantities: Jethalal started with 49 TV sets and ended with 69 TV sets.

2. Find the total increase: 69 - 49 = 20 TV sets were added in all.

3. Divide the total increase by the weekly rate of 5 sets: 20 / 5 = 4.

4. So the count rose from 49 to 69 over 4 weeks.

Cross-check: working forward, 49 + 4 x 5 = 49 + 20 = 69, which matches the stated final count of 69 sets, confirming four weeks is correct.