The table shows how much Tiffany saves daily. For each subsequent day, she saves $9 more than the previous day.
- How much will Tiffany save on Day 4?
- On which day will Tiffany save $109?
- How much savings will Tiffany have in total by the day found in part (b)?
(a)
Pattern for the amount saved
Day 1: 1 x 9 + 10 = $19
Day 2: 2 x 9 + 10 = $28
Day 3: 3 x 9 + 10 = $37
Day 4: 4 x 9 + 10 = $46
Formula
Amount saved = Day Number x 9 + 10
Amount saved on Day 4
= 4 x 9 + 10
= $46
(b)
Number of days that Tiffany takes to save $109
= (109 - 10) ÷ 9
= 99 ÷ 9
= 11
(c)
Total savings that Tiffany saves by Day 11
= 19 + 28 + ... + 100 + 109
= (19 + 109) x (11 ÷ 2)
= 128 x 5.5
= $704
Answer(s): (a) $46; (b) 11; (c) $704