The table shows how much Risa saves daily. For each subsequent day, she saves $3 more than the previous day.
- How much will Risa save on Day 5?
- On which day will Risa save $61?
- How much savings will Risa have in total by the day found in part (b)?
(a)
Pattern for the amount saved
Day 1: 1 x 3 + 10 = $13
Day 2: 2 x 3 + 10 = $16
Day 3: 3 x 3 + 10 = $19
Day 4: 4 x 3 + 10 = $22
Formula
Amount saved = Day Number x 3 + 10
Amount saved on Day 5
= 5 x 3 + 10
= $25
(b)
Number of days that Risa takes to save $61
= (61 - 10) ÷ 3
= 51 ÷ 3
= 17
(c)
Total savings that Risa saves by Day 17
= 13 + 16 + ... + 58 + 61
= (13 + 61) x (17 ÷ 2)
= 74 x 8.5
= $629
Answer(s): (a) $25; (b) 17; (c) $629