If the bucket is 2 pounds when it is half full, you have to determine how many dimes are in the bucket and multiply by two. We know that the empty bucket is .2 pounds, so you subtract the weight of the empty bucket from the 2 pounds to leave you with the weight of just the dimes.
2 pounds (the weight of the half-full bucket) minus 0.2 pounds (the weight of the empty bucket)=1.8 (current weight in dimes).
There are 1.8 pounds of dimes, but there are 200 dimes in 1 pound. Multiply the two numbers to get the current number of dimes.
1.8 x 200=360 (dimes in the half bucket). Multiply this by 2 to get the number of dimes if the bucket was full.
360x2=720 dimes. John will have $72.