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Estimate these

Estimate these

This task is about estimation with addition and multiplication.

In each box below clearly show how you worked out your best estimate.

a)

Card A: Estimate the total cost of 1 first aid kit, 1 store tent, and 1 torch. Estimate, do not do an exact calculation.

My estimate is: ____________________

b)

Card B: Estimate the total cost of 40 tins of tomatoes and 20 loaves of bread. Estimate, do not do an exact calculation.

My estimate is: ____________________

c)

Card C: Estimate the total cost of 3 utensil sets, 8 batteries, 2 water bottles, and 5 gas cookers. Estimate, do not do an exact calculation.

My estimate is: ____________________

d)

Card D: Estimate how much it cost each of the 9 people for the kayaking lesson, assuming they all paid the same amount. Estimate, do not do an exact calculation.

My estimate is: ____________________

e)

Card E: Energy bars come in boxes of 48. Each bar costs $2.05. Estimate how much each person pays if the cost is equally shared between 18 people. Estimate, do not do an exact calculation.

My estimate is: ____________________

Card A
Estimate the total cost of one first aid kit, one store tent and one torch.

$205.23

$37.65

$13.95

Card B
Estimate the total cost of 40 tins of tomatoes and 20 loaves of bread.

97 cents each

$1.52 each

Card C
Estimate the total cost of 3 utensil sets, 8 batteries, 2 water bottles and 5 gas cookers.

$10.54 each

$1.53 each

$23.85 each

$19.25 each

Card D
The kayaking lesson came to a total of $425 for 9 people. Estimate how much it cost each person for the lesson, assuming they all paid the same amount.

Card E
Energy bars come in boxes of 48. Each bar costs $2.05. Estimate how much each person pays if the cost is equally shared between 18 people.

$2.05 each

Task administration:

This task is completed with pencil and paper only.

Equipment:

Pencil and paper; Task Cards (A to E); Student worksheet

This task assesses a students' ability to use an accurate method of estimation to calculate costs.
Assessments can be carried out with one student at a time or with a group/class of students using an OHP. If done 'one-on-one', the students may respond orally to how they got their estimate, rather than writing down an explanation of their estimation method on the Student Worksheet provided.
Before starting, it is important to emphasise to the student/s that this is an estimation task, and therefore they will be assessed on their method of estimation rather than their ability to calculate the correct answer. It will become apparent in their workings/explanations if they are making exact calculations, rather than estimating.
The teacher is to read out the following instructions:
In this activity you are going to be estimating the cost of various things the Camping Club has to purchase for their trip.
You must clearly show each step in working out your best estimate on the worksheet provided. You will be assessed on how you got your estimate, rather than calculating the correct answer. You will not be able to use calculators.

Show the student/s Card A and say,
Write down your estimate of the total cost of one first aid kit, one store tent, and one torch. Clearly show (or explain) what you did to get your estimate.
Show the student/s Card B and say,
Write down your estimate of the total cost of 40 tins of tomatoes and 20 loaves of bread. Clearly show (or explain) what you did to get your estimate.
Show the student/s Card C and say,
Write down your estimate of the total cost of 3 utensil sets, 8 batteries, 2 water bottles, and 5 gas cookers. Clearly show (or explain) what you did to get your estimate.
Show the student/s Card D and say,
Nine of the people camping decided to pay for a kayaking lesson which came to a total of $425. Estimate how much it cost each person for the lesson, assuming they all paid the same price. Clearly show (or explain) what you did to get your estimate.
Show the student/s Card E and say,
The trampers in the group bought a box of energy bars. Each box holds 48 bars, and each bar cost $2.05. Estimate how much each person pays if the cost is equally shared between 18 people.

Answers/responses:

2 marks or 1 mark	a)	Satisfactory estimate given based on an acceptable method of estimation. (The exact calculation is $256.83), e.g., estimate of $255; the sum of rounding the first aid kit up to $40, rounding the tent down to $200, and rounding the torch up to $15. Acceptable method but 1 error made, including: a rounding error,* or a calculation error.
2 marks or 1 mark	b)	Satisfactory estimate given based on an acceptable method of estimation. (The exact calculation is $69.20), e.g., estimate of $70; rounding the tomatoes up to $1 and multiplying by 40, rounding the bread down to $1.50 and multiplying by 20, and taking the sum of these. Acceptable method but 1 error made, including: a rounding error,* or a calculation error.
2 marks or 1 mark	c)	Satisfactory estimate given based on an acceptable method of estimation. (The exact calculation is $187.81), e.g., estimate of $192; rounding the utensil set down to $10 and multiplying by 3, rounding the batteries down to $1.50 and multiplying by 8, rounding the water bottles up to $25 and multiplying by 2, and rounding the gas cookers up to $20 and multiplying by 5, and taking the sum of these. Acceptable method but 1 error made, including: a rounding error,* or a calculation error.
2 marks or 1 mark	d)	Satisfactory estimate given based on an acceptable method of estimation. (The exact calculation is $47.22), e.g., estimate of $42; rounding the cost of the lesson down to $420 and dividing this by the rounded up figure of 10. Acceptable method but 1 error made, including: a rounding error,* or a calculation error.
2 marks or 1 mark	e)	Satisfactory estimate given based on an acceptable method of estimation. (The exact calculation is $5.47), e.g., estimate of $5, rounding the number of bars up to 50 and multiplying the cost per bar (rounded down to $2) to get $100. Then divide $100 by 20 (the number of people rounded up to 20). Acceptable method but 1 error made, including: a rounding error,* or a calculation error.

* NOTE: Final estimates will vary due to variations in estimation methods used. You should be looking for a logical and sensible method of estimation. No mark to be awarded for exact calculations.
** NOTE: A rounding error includes instances when a student has rounded up or down inappropriately, e.g., rounding 97c to 90c rather than $1.00 or rounding $13.95 to $20.00 rather than $15.00.