Question 426628
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Hi
Let x represent how the block weighed to begin with
Question states***
 x - x/3 - (1/3)(x/3) = 40lb    |loses one third of its weight every hour
Solving for x
 x - x/3 - x/9 = 40
 9x - 3x - x = 360
       5x = 360
        x = 72lbs, original weight of the block

CHECKING our Answer***
   72lb - 24lb - 8lb = 40lbs