Figure 1 shows a plate and Figure 2 shows two stacks of identical plates. There are 3 plates in a shorter stack and 7 plates in a taller stack. The height of the shorter stack is 20 cm and the height of the taller stack is 44 cm.

  1. (a)

    Find the height of a plate.

  2. (b)

    Matthew wants to pack the plates as a single stack into a box 1 m high. Figure 3 shows the 2 possible arrangement A and B. Which arrangement will allow Matthew to pack more plates? How many more?

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Worked solution

17(a)

1. Identify the difference in height and the difference in the number of plates between the two stacks.

Difference in height =44−20=24= 44 - 20 = 24 cm
Difference in number of plates =7−3=4= 7 - 3 = 4 plates

2. Calculate the height of one plate gap (the thickness added by each additional plate).

Height of 1 gap =24÷4=6= 24 \div 4 = 6 cm

3. Calculate the height of a single plate by subtracting the gaps from the total height of a stack.

Height of 3 plates stack =20= 20 cm
This stack consists of 1 base plate and 2 gaps.
Height of 2 gaps =2×6=12= 2 \times 6 = 12 cm
Height of 1 plate =20−12=8= 20 - 12 = 8 cm

Answer

88 cm

17(b)

1. Find the height of a single plate and the height added by each subsequent plate in a normal stack.

From the given stacks:
Height of 7 plates = 4444 cm
Height of 3 plates = 2020 cm
Difference in height for 4 plates = 44−20=2444 - 20 = 24 cm
Height added by each additional plate in a stack = 24÷4=624 \div 4 = 6 cm
Height of the first plate = 20−2×6=820 - 2 \times 6 = 8 cm

2. Calculate the maximum number of plates that can be packed in Arrangement A.

In Arrangement A, the plates are stacked normally.
Let nn be the number of plates.
Total height = 8+6(n−1)=6n+28 + 6(n - 1) = 6n + 2 cm
We need the height to be at most 11 m = 100100 cm.
6n+2≤1006n + 2 \le 100
6n≤986n \le 98
n≤16.33n \le 16.33
So, a maximum of 1616 plates can be packed in Arrangement A.

3. Calculate the maximum number of plates that can be packed in Arrangement B and find the difference.

In Arrangement B, the plates are in an alternating orientation (e.g., top-to-top, base-to-base), meaning they do not overlap and each plate contributes its full height of 88 cm.
Number of plates in Arrangement B = 100÷8=12.5100 \div 8 = 12.5
So, a maximum of 1212 plates can be packed in Arrangement B.
Difference = 16−12=416 - 12 = 4
Arrangement A allows Matthew to pack 44 more plates.

Answer

Arrangement A, 4 more plates

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