Zara fences off a piece of land next to a wall to make a vegetable garden. [Figure 6.1] The garden is a rectangle with the wall as one side of the rectangle. The area of the garden is 18 square metres. The width of the garden is x metres. (a) The total length of fencing required for the garden is y metres. Show that y = 2x + 18/x.
- (a)The total length of fencing required for the garden is y metres. Show that y = 2x + 18/x.[1]
- (b)(i)Complete the table for y = 2x + 18/x. [Table: x values 1, 2, 3, 4, 5, 6, 7, 8, 9. y values missing for x=1, 2, 9, and given for 3, 4, 5, 6, 7, 8 as 12, 12.5, 13.6, 15, 16.6, 18.3 respectively.][2]
- (b)(ii)On the grid, draw the graph of y = 2x + 18/x for 1 ≤ x ≤ 9. [Figure 6.2][3]
- (c)Use your graph to find the two possible widths of the garden if 14 metres of fencing is used.[2]
- (d)(i)The fencing costs $20 per metre. Find the minimum amount it will cost Zara to build the fence.[2]
- (d)(ii)Zara wants to spend no more than $350 on the fence. Find the greatest possible width of the garden Zara can make.[2]
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Mark scheme
Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.
- [1] Acceptable justification eg Length = 18/x leading to answer or y = x + x + 18/x
- [2] B1 for two correct values
- [3] B2FT for 8 or 9 points correctly plotted or B1FT for 6 or 7 points correctly plotted
- [2] FT reading their graph at y = 14 Tolerance ± 1 mm
- [2] B1FT for one correct
- [2] B1 for y = 12 soi
- [2] B1 for 17.5 soi
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