If a boy and a half can eat a hotdog and a half in a minute and a half; how many hotdogs can 6 boys eat in 6 minutes?

1.5 boys eat 1.5 hot dogs in 1.5 minutes

1.5 boys = 1.5 hot dogs / 1.5 minutes = 1 hot dog / minute

6 boys = 4*1.5 boys = 4*1 hot dog / minute = 4 hot dogs / minute

6 hot dogs / (4 hot dogs / minute) = 6 hot dog minutes / 4 hot dogs = 3 hot dog minutes / 2 hot dogs = 3/2 minutes = 1.5 minutes