After paying the money, I will return 3 yuan, which is like this:

27+3=30 yuan

Among them, the innkeeper in 27 yuan only took 25 yuan, and 2 yuan was detained by the waiter.

So the correct answer to the question is 25 (money received by the boss) +2 (money withheld by the waiter) +3 (money returned to the passengers) =30 yuan, not 27+2, but 27+3, so 1 yuan is added incorrectly.

Mathematics learning in lower grades

In class, first of all, we should pay attention to guiding students to observe, summarize and sort out the structural characteristics and counting characteristics of abacus, and make simple abacus by using the existing materials around us. In the activities of making abacus, students observe with their eyes, operate with their hands, think with their brains, and tell with their mouths, thus stimulating their thinking and imagination in relaxed and pleasant practical activities.

Teachers who have taught first-grade mathematics know that the composition of numbers within 10 is an important basis for understanding numbers, establishing the relationship between numbers and calculating addition and subtraction, so recitation is the key.

The composition of 10 is one of the key and difficult points. Children's songs can be used in teaching, such as "19 19 good friends, 2828 walk together, 3737 hold hands, 4666 don't let go, 550 make a hand". With the help of music rhythm and body language, boring recitation becomes catchy and interesting.