Make Andy's units the same in both ratios to compare Mother and Father directly.<br><br>
• Andy : Father = 3 : 4 = 12 : 16<br>
• Andy : Mother = 4 : 5 = 12 : 15<br>
• So Andy : Mother : Father = 12 : 15 : 16<br>
• Mother : Father = 15 : 16<br><br>
Final Answer: 15 : 16