ok so there are 2 ppl in this scenario… one of which has half the amount of the other… there for we can divide this TOTAL amount (1,080) by 3
1080 divided by 3 is 360
so her sister has 360 stamps
there r still 2 groups of the problem remaining (360 and 360)
and since her sister was half of what she has.. and her sister has 360
we must add 360 to 360
so the answer is 720
