On Serena's tenth birthday her mom was 3 tines Serena's age. how old will Serena and her mom be when her Moms age 0.5 will equal Serena's age

Mom is 30 years old when Serena is 10 because 10 x 3 = 30.

They are 20 years apart. [This is key]

Half (.5) of mom's age will be = to Serena's age.

Therefore, when mom is 40 years old, Serena is 20 years old.

We can see that half of 40 = 20.

Hope this makes sense!