Lizzy: A tree had 1000 leaves before the onset of the dry season, when it sheds all its leaves. In the first week of the dry season, the tree shed 2/5 of the leaves. In the second week, it shed 40% of the remaining leaves. In the third week, the tree shed 3/4 times as many leaves as it shed on the second week. Calculate the number of leaves the tree hadn't shed by the third week..
Me: Hmmm, let me think. I think this is the detailed solution:
In the first week, the tree shed 2 / 5 * 1000 = 400 leaves. The number of leaves remaining on the tree at the end of the first week is 1000 - 400 = 600. In the second week, the tree shed 40 / 100 * 600 = 240 leaves. The number of leaves remaining on the tree is 600 - 240 = 360. The third week the tree shed 3 / 4 of its leaves, a total of 3 / 4 * 360 = 270 leaves. The number of leaves remaining on the tree is 360 - 270 = 90 leaves. Final answer: 90.