3/4 of the number of lollipops are grape flavored in order for the
probability of choosing one to be 3/4.
There must be a whole number of lollipops.
3/4 of 16 is 12, a whole number, so there could be 16 lollipops.
3/4 of 28 is 21, a whole number, so there could be 28 lollipops.
3/4 of 49 is 36.75, NOT a whole number, so there could NOT be 49 lollipops.
3/4 of 144 is 108, a whole number, so there could be 144 lollipops.
Edwin