Buying surfing gear

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This task is about including and excluding sales tax.

Raedon wants to buy some surfing gear. He needs to know whether the sales tax is included or excluded.

Question 1Change answer

a) Raedon likes a surfboard that is priced at $360 excluding sales tax of 12.5%.

How much sales tax would he pay on this surfboard? $

b) He then sees another surfboard that is priced at $480 excluding sales tax of 12.5%.

What is the total price he would pay for this surfboard? $

c) Raedon tries on a wetsuit that costs $180 including sales tax of 12.5%.

How much sales tax has been included in the total price of $180? $

d) Raedon then sees another wetsuit that costs $279 including sales tax of 12.5%.

What was the price of the wetsuit before the sales tax was added? $

Task administration:

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Description of task:

Students solve number problems involving prices which include and exclude sales tax.

Learning Progression Frameworks

This resource can provide evidence of learning associated with

within the Mathematics Learning Progressions Frameworks.

Answers/responses:

Diagnostic and formative information:

	Common error	Likely calculation	Likely reason
a) b)	28.80 518.40	360 × 0.08 480 × 1.08	Treats sales tax as 1/8 to be added onto the price and represents this as 0.08.
c) d)	22.50 244.13	180 × 0.125 279 × 0.875	Deducts sales tax as 1/8 of total price rather than 1/9th.
c) d)	14.40 256.68	180 × 0.08 279 - 279 × 0.08	Treats sales tax as 1/8 of total price and represents this as 0.08.
b) d)	492.50 265.50	480 + 12.5 279 - 12.5	Treats 12.5% as $12.50.