This lecture mainly introduces simple application problems solved by addition and subtraction.

Example 1 Xiaoling has 46 ducks and 24 chickens at home, and the total number of chickens and geese is 5 more than that of ducks. How many geese are there in Xiaoling's house?

Solution: The known conditions are shown as follows:

The expression is: 24+? =46+5。 From this, we can draw the conclusion that keeping geese is (46+5)-24=27 (only).

A: There are 27 geese.

If the total number of chickens and geese in example 1 is 5 less than that of ducks (other things unchanged), the known conditions can be expressed as follows.

The expression is: 24+? +5=46。 From this, it can be concluded that the goose raising rate is 46-5-24= 17 (only).

There are 52 apples in one basket and some pears in the other. If you take 18 pears from the pear basket, there are fewer pears than apples 12. How many pears are there in the pear basket?

Analysis: According to the known conditions, various quantitative relations are shown in the following figure.

There are several ways of thinking:

(1) According to the fact that 18 pears are removed, there are fewer pears than apples 12. First find out the existing pears in the pear basket (52- 12=40), and then find out the original pears (52- 12)+ 18 =.

(2) According to 18 pears, there are fewer pears than apples 12. If we take less 12 pears, there are 52 pears as many as apples. In this way, there are more original pears than apples 18- 12=6 (pieces), and then the original pears are 52+( 18- 12)=58 (pieces).

(3) According to taking 65,438+08 pears, there are 65,438+02 fewer pears than apples. We assume that only 65,438+08 apples are added in the apple basket without taking pears, and there are 52+65,438+08 apples = 70 apples.

In this way, there are more apples than the original pears 12 (see the picture below). From this, the original pear can be obtained (52+ 18)- 12=58 (pieces).

From the above three different angles, the following three solutions are obtained.

Solution1:(52-12)+18 = 58 (pieces).

Solution 2: 52+( 18- 12) = 58 (pieces).

Solution 3: (52+ 18)- 12 = 58 pieces.

There are 58 pears in the pear basket.

Class 1, Grade 3, a school bought some sweets to welcome the children hand in hand. It is known that fruit candy is more than white rabbit soft candy 15, and chocolate candy is more than fruit candy by 28. It is also known that the number of chocolate candy bars is exactly twice that of white rabbit fudge bars. How many sweets did Class 1, Grade 3 buy?

Analysis and solution: as long as the number of blocks of one sugar is found, the number of blocks of the other two sugars can be found according to the known conditions, and the total number of blocks can be found. What kind of sugar is the easiest to find first? Let's first express the known conditions as the following figure.

As can be seen from the above figure,

The number of small white rabbit soft candy blocks = 15+28=43 (blocks),

The number of fruit candy blocks =43+ 15=58 (blocks),

The number of chocolate candy =432=86 (bars).

Total number of sweets =43+58+86= 187 (block).

A: * * * bought 187 candy.

A dry well is 230 cm deep, and a snail has to climb from the bottom to the wellhead. It climbs 1 10 cm every day, but it drops 70 cm at night. When can this snail climb out of the wellhead?

Analysis and solution: Because the snail has to climb 1 10 cm on the last day, the distance that the snail has to climb a few days ago is 230 cm deep, minus this 1 10 cm (equal to 120 cm). Because snails climb 1 10 cm in the daytime and 70 cm down at night, they climb 1 10-70=40 cm every day.

Because 12040=3, 120cm was crawled by a snail three days ago. So the snail can climb to the wellhead on the fourth day.

If the depth of the dry well in Example 4 is changed to 240 cm, and other figures remain unchanged, when can this snail climb out of the wellhead? (Day 5)

Exercise:

1. A, B and C each ate a few peaches. After A gave B 2 peaches, B gave C 3 peaches, and C gave A 5 peaches, all three people had 9 peaches. How many peaches are there in A, B and C?

2. Three bridges, the first one is 287m long, the second one is 85m longer than the first one, and the third one is shorter than the total length of the first and second one142m. How long is the third bridge?

3.( 1) There are 40 chocolate candy bars and some milk candy in the kindergarten class. After giving the child 24 pieces of toffee, the toffee is less than the chocolate candy 10. How much is the original toffee?

(2) There are 48 pieces of chocolate candy and some milk candy in the kindergarten middle class. Give the child 26 pieces of toffee, which is only more than chocolate candy 18 pieces. How much is the original toffee?

4. A barrel of diesel oil weighs 120kg. After using half of the diesel oil, the barrel weighs 65kg. How many kilograms of diesel are there in this bucket? How much does an empty bucket weigh?

5. A snail climbed from a low water bottom to the wellhead, climbed 1 10 cm during the day, and dropped 40 cm at night. At the end of the fifth day, the snail arrived at the wellhead. How deep is this dry well? If you climb to the wellhead during the day on the fifth day, how many centimeters is this well at least? (excluding the length below cm)

6. On a straight line, point A is 20mm to the left of point B, point C is 50mm to the left of point D, and point D is 40mm to the right of point B ... Write the order of these four points from left to right.

7.( 1) The sum of five different numbers is 172. The smallest of these numbers is 32. What's the biggest number?

(2) The sum of six different numbers is 356. Among these figures, the largest is 68. What's the smallest number?

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