When a bakery opened this morning, the ratio of the number of pineapple muffins to mango muffins was 3:2. After 144 pineapple muffins were sold, the ratio of the number of pineapple to mango muffins changed to 3:5. How many pineapple muffins were there when the bakery opened this morning?

So

pinaple:mango=3:2

after 144 pinaple was sold (-144 pinaple)

the ratio changed to 3:5

one way is to convert the second number of both ratios to the same number, since they (mangos) didn't change

3:2=15:10

3:5=6:10

so

15 pinaple units-144=6 pinaple units

add 144 to both sides

15p=6p+144

subtract 6p (pinaple units) from bothsides

9p=144

divide both sides by 9

pinaple unit=16

there were 15 units in the begining so

in the beginning, ther were 15 times 16 pinaples or 240 pinaple muffins

240 is the answer