Isabella is twice as old as Antonio.  In 18 months, she will be 10 years old.  How many months old is Antonio?
How old will Isabella be at age 10? ** First, we determine that Isabella will be 10*12= <<10*12=120>>120 months old at age 10, to find a number to compare her age to Antonio's with.
How old is Isabella currently? ** Then we subtract the 18 months from the total of 120 months to find 120-18= <<120-18=102>>102 months, which is the age Isabella is currently.
How old is Antonio? ** Since at 102 months old Isabella is twice as old as Antonio, we take 102/2= <<102/2=51>>51 months as Antonio's age.
#### 51