A radioactive chemical decays 20% each day. If 48 pounds of this chemical remain today, how many pounds of this chemical were present two days ago?
Can you show work please, so I understand?
Thanks!
Can you show work please, so I understand?
Thanks!
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48lbs / .80 = 60 lbs -----yesterday
60 lbs / .80 = 75 lbs ----two days ago
that was the easy way
the REAL way
take 20% of 48 and ADD that to 48. (48*.20) = 12lbs 12 + 48 = 60lbs
Take 20% of 60 and ADD that to 60 (60*.20) = 15lbs 15 + 60 = 75lbs
60 lbs / .80 = 75 lbs ----two days ago
that was the easy way
the REAL way
take 20% of 48 and ADD that to 48. (48*.20) = 12lbs 12 + 48 = 60lbs
Take 20% of 60 and ADD that to 60 (60*.20) = 15lbs 15 + 60 = 75lbs
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Suppose two days ago there were x pounds.
After one day, there are x - 0.2x = 0.8x left.
After another day, there are (0.8x) - 0.2*(0.8x) = 0.64x left.
0.64x = 48 pounds.
x = 48 / 0.64 = 74 lb.
After one day, there are x - 0.2x = 0.8x left.
After another day, there are (0.8x) - 0.2*(0.8x) = 0.64x left.
0.64x = 48 pounds.
x = 48 / 0.64 = 74 lb.