There are two explanations:

4 1+ 19= This kind of problem is easy to calculate. Single digits+single digits is exactly 10, and the calculation result is 60. This kind of topic is not skilled, and it needs to be calculated vertically.

Questions like 79-33 do not need to be borrowed. A vertical subtraction can be solved quickly. If you subtract one digit from one digit, you will write one digit, and if you subtract ten digits from ten digits, you will write ten digits.

Extended data:

Addition has several important properties. It is interchangeable, which means that the order is not important, it is interrelated, which means that when more than two numbers are added, the order in which the addition is performed is not important. Repeatedly adding 1 is the same as counting; Adding 0 will not change the result. Addition also follows related operations such as subtraction and multiplication.

Addition is one of the simplest digital tasks. The most basic addition: 1+ 1 five-month-old babies and even other animal species can be counted. In primary education, students are taught to calculate the superposition of decimal numbers, starting with one digit, and gradually solving the more difficult number calculation.

Generally speaking, the binary relation "+"is defined on the set f, which satisfies:

Ⅰ? Law of exchange: for arbitrary? Answer? ，b？ ∈? f？ ，a？ +? b？ =? b？ +? Answer? ∈? f；

Ⅱ? Law of association: for any a, b, c∈F, a? + (b？ +c) = (a？ +b)+c；

Ⅲ? Unit element: There is an element 0 ∈? f？ , satisfy any one ∈? f？ ，a？ + 0 = 0 +? Answer? =? a；

Ⅳ inverse element: for any? Answer? ∈F？ , there is an element-a ∈? f？ , meet one? + (-a) = 0 .

References:

Baidu Encyclopedia-Supplement