Four friends John, Jenita, Maria, and Julie each choose a ball in a different favorite colour: yellow, violet, green, or red. Using the given clues, what is Maria favorite colour?

Introduction / Context:
This is a classic logical deduction puzzle involving four people and four different favourite colours. The friends John, Jenita, Maria, and Julie each like one unique colour among yellow, violet, green, and red. Several clues restrict which person can like which colour. The question specifically asks for Maria favourite colour. Solving this puzzle tests your ability to manage multiple constraints, eliminate possibilities, and arrive at a consistent assignment of colours to people.

Given Data / Assumptions:

• The four people are John, Jenita, Maria, and Julie.
• The four favourite colours are yellow, violet, green, and red, with each colour chosen by exactly one person.
• John and Maria do not like violet, so violet cannot be the favourite colour of John or Maria.
• The person who likes red is a girl, so red must belong to Jenita, Maria, or Julie, not to John.
• Jenita likes green, but green is not her favourite colour.
• Jenita favourite colour is either green or yellow, but she can have only one favourite colour.
• John likes red, but red is not his favourite colour.

Concept / Approach:
The main concept is systematic elimination. You must interpret likes as general preference and favourite as the one final colour assigned to a person. First, you use the clues about what cannot be someone favourite. Then you use the either or but not both type of clue for Jenita to fix her favourite colour. Once one person favourite colour is fixed, you can assign the remaining colours step by step, always respecting that each colour is used exactly once. Finally, you read off which colour ends up with Maria.

Step-by-Step Solution:
Step 1: From the clue that Jenita favourite colour is either green or yellow and the clue that green is not her favourite, conclude that Jenita favourite colour must be yellow. Step 2: Assign yellow to Jenita as her unique favourite colour. This means yellow is no longer available for John, Maria, or Julie. Step 3: Now consider John. John does not like violet and red is not his favourite colour, so John favourite colour cannot be violet or red. Step 4: The remaining colours after assigning yellow to Jenita are violet, green, and red. Since John cannot have violet or red, the only colour left for John favourite colour is green. Step 5: Assign green as John favourite colour. Now yellow is taken by Jenita, and green is taken by John, leaving violet and red for Maria and Julie. Step 6: From the clue that John and Maria do not like violet, you know that Maria favourite colour cannot be violet. Step 7: Since only violet and red remain, and Maria cannot have violet, Maria must have red as her favourite colour. Therefore, Julie must have violet as her favourite colour.
Verification / Alternative check:
To verify, list the final assignments: Jenita favourite colour is yellow, John favourite colour is green, Maria favourite colour is red, and Julie favourite colour is violet. Check all clues: John and Maria do not like violet (neither of them has violet), the person who likes red is a girl (Maria is a girl and has red), Jenita likes green but it is not her favourite colour (green belongs to John, not to Jenita), Jenita favourite is either green or yellow and we have chosen yellow, and John likes red but it is not his favourite colour (red is Maria favourite). All clues are satisfied, so the solution is consistent.

Why Other Options Are Wrong:
Yellow: Yellow is assigned to Jenita by the logical deduction and cannot also be Maria favourite colour.
Violet: Maria is explicitly said not to like violet, so violet cannot be her favourite colour.
Green: Green is forced to be John favourite colour because he cannot have violet or red and yellow is already taken.

Common Pitfalls:
A common mistake is to misinterpret likes as equal to favourite, which can cause confusion with the clues about Jenita and John liking colours that are not their final favourites. Another pitfall is not keeping track of which colours have already been assigned, leading to duplicate assignments. Drawing a simple table with people on one axis and colours on the other can help avoid such errors. Following each clue in order and updating the table systematically leads directly to the conclusion that Maria favourite colour is red.

Final Answer:
According to the clues, Maria favourite colour is Red.