Question:
Amanda, Bob and Caren went to a bakery to buy a birthday cake for their monther. They shared the cost of the cake equally. However, Amanda did not bring any money. Bob and Caren paid for the cake first. The ratio of the amount Bob paid to the amount Caren paid was 5 : 3. When they reached home, Amanda returned her share of the bill to Bob and Caren. She paid Bob $5.60.
a) How much did Amanda pay Caren?
b) How much did the birthday cake cost?
Solution:
![P6 / Rosyth / 2019 / SA1 / Paper 2 – Q15 [5 marks]](https://i0.wp.com/sgprimaths.com/wp-content/uploads/2020/05/P6_Rosyth_2019_SA1_Paper2_Q15-Qns.jpg?resize=400%2C216&ssl=1)
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I dont understand how u know B got 7
units more but C got 1unit more. I know those.add up
to A but how do u know B got 7u while C got 1u?
Hi Ka Yeung,
That’s a good question. Here’s the explanation.
(1) From the ratio of 5 : 3, we know that the total units = 8
(2) Because the bill was split equally among the 3 siblings, the total units must be a multiple of 3.
(3) Hence, we change the total units from 8 to 24.
(4) When total units = 24u, each sibling should pay 8u.
(5) Bob has paid 5 x 3 = 15u, which is 7u extra of 8u.
(6) Caren has paid 3 x 3 = 9u, which is 1u extra of 8u.
Hope this explanation helps!