Question 23 (5 marks) In a tropical drink, the ratio of pineapple juice to mango juice to orange juice is $15: 9: 4$. (a) How much orange juice is needed if the tropical drink is to contain 3 litres of pineapple juice?

Step 1 ：The ratio of pineapple juice to orange juice is 15:4. This means that for every 15 parts of pineapple juice, there are 4 parts of orange juice.

Step 2 ：If we have 3 litres of pineapple juice, we need to find out how much orange juice corresponds to this amount.

Step 3 ：Let's denote the ratio of pineapple juice to orange juice as \(\frac{15}{4} = 3.75\)

Step 4 ：Given that we have 3 litres of pineapple juice, we can calculate the amount of orange juice as follows: \(3 \times \frac{4}{15} = 0.8\) litres

Step 5 ：Therefore, the amount of orange juice needed is \(\boxed{0.8}\) litres.