If a teenager and a half can eat a pizza and a half in a day and a

Yep. Since one teenager can eat a pizza a day, then 12 teens should be able to eat 36 pizzas in 3 days.

Thank You.

You're welcome.

1.5 teens eat 1 pizza in 1.5 days

3 teens eat 2 pizzas in 1.5 days
3 teens eat 4 pizzas in 3 days
12 teens eat 16 pizzas in 3 days

Missed the half of the pizza

1.5 teens eat 1.5 pizza in 1.5 days
3 teens eat 3 pizzas in 1.5 days
3 teens eat 6 pizzas in 3 days
12 teens eat 24 pizzas in 3 days

The answer is 24.

You can set the problem up as fractions.
1.5 teens/1.5 pizzas = 1.5 days

the teens to pizza are 1:1. So you would say 1/1=1.5
then change it to 12/12 = 1.5 and you would multiple by 2 to get 3 days.
so 12*2 = 24

I am a pharmacist and the correct way to solve questions like this is think of RATE OF CONSUMPTION.

i.e. consumption = pizza/day
i.e. 1.5 TEENS = 1.5 PIZZA/1.5DAY = 1 pizza/day
the rest is simple maths.