This is a mathematical problem, please use the reduction method to calculate, and give the idea of solving the problem, There are 90 books in group A, B and C. group B borrows three books from group A and then lends five books to group C. as a result, the three groups have the same number of books. Q: how many books did group A, B and C have?

This is a mathematical problem, please use the reduction method to calculate, and give the idea of solving the problem, There are 90 books in group A, B and C. group B borrows three books from group A and then lends five books to group C. as a result, the three groups have the same number of books. Q: how many books did group A, B and C have?

There are 90 books in group A, B and C, with an average of 30
Group B borrowed three copies from group A and then lent five copies to group C. in fact, group B took out two copies and group a gave all three copies to group C
So C originally had 30-5 = 25
B originally had 30 + 2 = 32
A originally had 30 + 3 = 33 copies

There are four bags, red, white, green and yellow. The total weight is 81 kg. If the red bag is increased by 2 kg, the white bag is decreased by 2 kg, the green bag is multiplied by 2, and the yellow bag is divided by 2, the weight of the four bags is equal. Then, the red bag weighs () kg, the white bag weighs () kg, the green bag weighs () kg, and the yellow bag weighs () kg
+ +
o

According to the known conditions, four packets are set: red is X-2, white is x + 2, green is x / 2, yellow is x × 2
x-2+x+2+x/2+x×2=81
x=18
So they are 16 20 9 36