Is the following formula correct? Talk about the reason 42 + 65 + 58 + 35 = (42 + 58) + (65 + 35) 4 * 8 + 25 * 5 = 4 * 25 + 8 * 5

Is the following formula correct? Talk about the reason 42 + 65 + 58 + 35 = (42 + 58) + (65 + 35) 4 * 8 + 25 * 5 = 4 * 25 + 8 * 5

The first is addition, which uses the law of combination of addition. The second is wrong. Addition and multiplication can't be exchanged freely. For example, when you go shopping, the quantity and price of apples and bananas are different. You can't multiply the price of apples by the weight of bananas, but the price of bananas by the weight of apples

There are 84 students in two classes of grade 5. There are 58 students in 5 / 8 class and 3 / 4 class 2. How many students are there in each class

Hypothesis: the number of class 1 is x, and the number of class 2 is y
Then we can get the following formulas:
X + y = 84 → that is, x = 84-y
5 / 8 * x + 3 / 4 * y = 58 → that is, 5x + 6y = 464
The combination of the two formulas gives (84-y) + 6y = 464 → that is, y = 76
So, x = 8

Simple calculation 58.6 * 132-5.86 * 3.2

Original formula = 5.86 * 1320-5.86 * 3.2
=5.86*（1320-3.2）
=5.86*1316.8
=7716.448

(- 11.58x) x27.16 - (- 37.16) x11.58 can be calculated in a simple way, and if so, how

Original formula = 37.16 * 11.58-27.16 * 11.58
=（37.16-27.16）*11.58
=10*11.58
=115.8