Correct option is D
Solution:
On day 1, she adds ; 1 coin
On day 2, she will add 1 more coin as 1 coin is already there in it ( i.e already added 1 coin + 1 more coin = 2)
On day 3, she should add 2 more coin as 2 coins are already there in it ( i.e already added 2 coin + 2 more coin = 4)
On day 4, she should add 4 more coin as 4 coins are already there in it ( i.e already added 4 coin + 4 more coin = 8)
On day 5, she should add 8 more coin as 8 coins are already there in it ( i.e already added 8 coin + 8 more coin = 16)
On day 6, she should add 16 more coin as 16 coins are already there in it ( i.e already added 16 coin + 16 more coin = 32)
On day 7, she should add 32 more coin as 32 coins are already there in it ( i.e already added 32 coin + 32 more coin = 64)
On day 8, she should add 64 more coin as 64 coins are already there in it ( i.e already added 64 coin + 64 more coin = 128)
That means a piggy-bank can carry 128 coins
Now, is she starts with two coins she will take 7 days to fill the piggy-bank
On day 1, she adds ; 2 coin
On day 2, she will add 2 more coin as 2 coin is already there in it ( i.e already added 2 coin + 2 more coin = 4)
On day 3, she should add 4 more coin as 4 coins are already there in it ( i.e already added 4 coin + 4 more coin = 8)
On day 4, she should add 8 more coin as 8 coins are already there in it ( i.e already added 8 coin + 8 more coin = 16)
On day 5, she should add 16 more coin as 16 coins are already there in it ( i.e already added 16 coin + 16 more coin = 32)
On day 6, she should add 32 more coin as 32 coins are already there in it ( i.e already added 32 coin + 32 more coin = 64)
On day 7, she should add 64 more coin as 64 coins are already there in it ( i.e already added 64 coin + 64 more coin = 128)
Hence, clearly, it will take 7 days to fill the full piggy-bank
Hence, Option (d) is true
Final Answer:
(d) 7.
