The number of long skipping ropes in the school used to account for three-eighths of the total number of long and short skipping ropes, and later I bought 20 long skipping ropes. At this time, the number of long skipping ropes accounts for seven twelfth of the total number of long and short skipping ropes. How many long and short skipping ropes are there in the school?

Solution: Total number of existing long and short skipping ropes:

20/(7/ 12-3/8)

=20/5/24

=96

Number of long skipping ropes:

96*7/ 12=56

Number of short skipping ropes:

96-56=40

That is, 56 long jump ropes and 40 short jump ropes.