The child's friend sent a question: there are two barrels of oil, A barrel and B barrel, and the oil in A barrel is equivalent to 50% of that in B barrel. Pour 3 liters of oil from barrel b to barrel a. At this point, the oil in barrel A is equivalent to 80% of that in barrel B, so there is () liter of oil in barrel A..
? How to solve a seemingly difficult problem?
? Thinking first, simple and easy. Problems are not done in the way of problems. Go to the "bottom logic"!
Look at the problem together! !
? Event: Oil in barrel B is poured into a part of barrel A. ..
? ? General idea: No matter how the whole process falls, the sum of two barrels of oil remains unchanged.
? The unit 1 is a whole, and the sum of two barrels of oil can be regarded as the unit 1 here.
Convert percentages into proportional relationships.
? Start: A is 50% of B.
Understanding: A is 50% of B, and A is half of B.
? A is 1, b is 2, and a and b have two barrels of oil and three points.
? A barrel of oil is one third of the whole.
After the change: A is 80% of B.
Understanding: A is 80% of B, 8 shares, 10 shares.
? A is 8, b is 10, and a is 18.
? At this time, the oil in the barrel is 8/8 or 4/9 of the whole.
? Just look at the armored barrel. After pouring 3 liters into the armored barrel, the armor has changed from one-third to four-ninth, an increase of one-ninth.
3 liters is more than a barrel, and a barrel is one ninth more, so 3 liters corresponds to one ninth of the whole.
? ? Divide the integer in proportion, and divide 3 by 1/9 to get the integer 27.
27 points in three copies, one for A and two for B. The answer is 9.
You got it? A junior high school equation problem, applying mathematics overall thinking, easy ko.