Answer:
40 coins
Step-by-step explanation:
Note that
[tex]10=\underline{2} \cdot 5,\\ \\8=\underline{2} \cdot 2\cdot 2.[/tex]
To find the least common multiple you have to multiply all common multiplies and then multiply them by all factors that left. Thus,
[tex]LCM(10,8)=\underline{2} \cdot 5\cdot 2\cdot 2=40.[/tex]
This means that if Walt and Amy each have 40 coins, then Walt can make 4 stacks with 10 coins in each and Amy can make 5 stacks with 8 coins in each.