Liam had 5/7 as many 20-cent coins as 1-dollar coins in his piggy bank. Each time, four 20-cent coins and six 1-dollar coins were taken out from the piggy bank. In the end, only seven 20-cent coins and four 1-dollar coins were left in the piggy bank. How many more 1-dollar coins than 20-cent coins were there in the piggy bank at first?
Let the number of 1-dollar coins==D
Then the number of 20-cent coins==5/7D
Let the numbe of withdrwals ==N
D - 6N == 4...................(1)
5/7D - 4N ==7...............(2), solve for D, N
D ==91 - number of 1-dollar coins that he started with
5/7 x 91 ==65 - number of 20-cent coins that he started with.
91 - 65 ==26 - more 1-dollar than 20-cent coins in his piggy bank at the start.