Answer:
LCM
it will take 80 calls
Explanation:
The solution is LCM
the least common multiple of 10 and 8 are
10=10,20,30,40,50,60,70,80,90,........
8= 8,16,24,32,40,48,56,64,72,80,88..........
The least common multiple is 80
therefore it will take 80 callers to call in to win both the bills
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