GST, service charge and discounts questions with answers

Questions

1. Question 1Add 9% GST

   A bicycle costs $1,380 before GST. Find its price after 9% GST is added.

   Show the worked solution

   1. Step 1: Add 9% GST: what percentage of the price is paid? (in dollars)$\dfrac{109}{100} \times 1380 = 1504.20$The price after GST is $1504.20.
2. Question 2Restaurant bill: service charge, then GST

   The table shows the food a family ordered at a restaurant. A 10% service charge is added to the bill, and then 9% GST is charged on the total. Find the amount the family pays, correct to the nearest cent.

   Item	Price
   Chicken wings	$9.90
   Satay (10 sticks)	$12.00
   Iced lemon tea	$3.20
   Cereal prawns	$22.80

   Show the worked solution

   1. Step 1: Add up the bill (in dollars)$9.90 + 12.00 + 3.20 + 22.80 = 47.90$
   2. Step 2: Add the 10% service charge$47.90 \times \dfrac{110}{100} = 52.69$
   3. Step 3: Then add 9% GST on that total$52.69 \times \dfrac{109}{100} = 57.4321$$\approx 57.43$ (to the nearest cent)The family pays $57.43.
3. Question 3Discount, then GST

   A washing machine has a marked price of $480 before GST. During a sale it is sold at a 5% discount, and 9% GST is then added to the discounted price. Find the amount paid, correct to the nearest cent.

   Show the worked solution

   1. Step 1: Take off the discount first (in dollars)$\dfrac{95}{100} \times 480 = 456$
   2. Step 2: Then add 9% GST$456 \times \dfrac{109}{100} = 497.04$The amount paid is $497.04.
4. Question 4Find the price before GST

   The price of a laptop, including 9% GST, is $523.20. Find its price before GST.

   Show the worked solution

   1. Step 1: The price with GST is what percentage of the price before GST? (in dollars)$100\% + 9\% = 109\%$$109\% \rightarrow 523.20$
   2. Step 2: Find 1% (in dollars)$1\% \rightarrow \dfrac{523.20}{109} = 4.8$
   3. Step 3: Find 100%: the price before GST$100\% \rightarrow 4.8 \times 100 = 480$The price before GST is $480.
5. Question 5Discount, then service charge, then GST

   The table shows the food a family ordered at a restaurant. Members get a 5% discount on the food, then a 10% service charge is added, and then 9% GST is charged on the total. The family are members. Find the amount they pay, correct to the nearest cent.

   Item	Price
   Fish and chips	$14.60
   Roti prata set	$6.60
   Chendol	$4.40

   Show the worked solution

   1. Step 1: Add up the food (in dollars)$14.60 + 6.60 + 4.40 = 25.60$
   2. Step 2: Take off the member discount first$25.60 \times \dfrac{95}{100} = 24.32$
   3. Step 3: Then add the 10% service charge$24.32 \times \dfrac{110}{100} = 26.752$
   4. Step 4: Then 9% GST on that total; round to the cent at the end$26.752 \times \dfrac{109}{100} = 29.15968$$\approx 29.16$ (to the nearest cent)The family pays $29.16.
6. Question 6Work back to the discount percentage

   The table shows the food a family ordered at a restaurant. Members get a discount on the food, then a 10% service charge is added, and then 9% GST is charged on the total. The family are members, and their final bill is $71.94. Find the percentage discount for members.

   Item	Price
   Chilli crab	$45.00
   Salted egg prawns	$26.00
   Fried kway teow	$9.00

   Show the worked solution

   1. Step 1: Add up the food (in dollars)$45.00 + 26.00 + 9.00 = 80$
   2. Step 2: Work backwards: take off the GST (the bill is 109% of the amount before GST)$\dfrac{71.94}{109} \times 100 = 66$
   3. Step 3: Then take off the service charge (110%)$\dfrac{66}{110} \times 100 = 60$
   4. Step 4: The discount, as a percentage of the food's price$\dfrac{80 - 60}{80} \times 100\% = 25\%$Members get a $25\%$ discount.