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Sinead problem is impossible because if he put one £1 coin in one pocket and then £2 in one pocket etc, then by the eight pocket he's put in £36. If Sinead put £9 in the next pocket he would of ran out of money. For his requirement, he would of needed £54.
Abbie problem is impossible because the towers she wants to build can't be equal because if one tower has 1,4,5 and 8 and the other tower has 2,3,6 and 7 it would be equal but there's 9 and 10 left so if they added them, the measurements wouldn't be equal. For them to be equal, Abbie would need 1 11cm cube and 1 12cm cube.
Eustace problem is impossible because the answer will be 2 above or 2 below the total e.g 1+2+3+4=10 5=+6+7+8=26 etc.