Giving marbles across does not change the total (60 + 9 = 69). In the end Bob = twice Nick, so Nick = 1 unit, Bob = 2 units, 3 units in all.<br><br>[[model:questions/solutions/q4152.png]]<br><br>• Total → 60 + 9 = 69 (unchanged)<br>• 3 units → 69<br>• 1 unit (Nick after) → 69 ÷ 3 = 23; Bob after = 46<br>• Bob gives → 60 − 46 = 14<br><br>Bob must give Nick 14 marbles.<br>Check: Bob 46, Nick 23, 46 = 2 × 23, total 69. ✓