The problem of less than
1.1. Knowledge to remember
The solution to the problem has less to do with one quantity than another.
1.2. Math form
General math: The problem requires finding the value of quantity A, knowing the value of B and A having a value less than B n units.
– Read and analyze the topic.
– Determine the quantity with large and small values, the relationship between the quantities. Usually, to find the value of a smaller quantity, we use subtraction.
– Present the solution to the problem.
– Check the results you just found.
1.3. Solving Textbook Exercises Page 30
Mai’s garden has 17 orange trees, Hoa’s garden has 7 oranges less than Mai’s garden. How many orange trees are there in Hoa’s garden?
To find the solution, we subtract 7 orange trees from Mai’s house.
The number of orange trees in Hoa’s garden is:
17 – 7 = 10 (orange tree)
Answer: 10 orange trees.
An is 95cm tall, Binh is 5cm lower than An. How many centimeters tall is Binh?
An : 95cm
Lower than An: 5cm
To find the solution, we subtract 5cm from An’s height.
The height of the jar is:
95 – 5 = 90 (cm)
Answer: 90 cm.
Class 2A has 15 girls, the number of boys in the class is 3 less than the number of girls. How many boys are there in class 2A?
Girl: 15 students
Less boys than girls: 3 friends
Boy: … student?
To find the solution, we subtract 3 girls from the number of students.
The number of boys in class 2A is:
15 – 3 = 12 (students)
Answer: 12 students.
1.4. Textbook exercise solution page 31
– How many stars are there in the circle?
– How many stars are there in the square?
– How many stars are there in a square than in a circle?
– How many stars are there in a circle less than in a square?
b) How many more stars must you draw in the circle so that the number of stars in the two shapes is the same?
– Count the number of stars in circles and squares.
– Subtract the number of stars in the square from the number of stars in the circle.
– Draw more stars with the result of the subtraction just calculated.
a) – In the circle there are 5 stars.
– There are 7 stars in the square.
– There are more stars in the square than in the circle (7 – 5 = 2)
– In the circle there are less than 2 stars in the square (7 – 5 = 2)
b) You have to draw 2 more stars inside the circle so that the number of stars in the two shapes is equal
Solve the problem according to the following summary:
English: 16 years old
I’m 5 years older than you
Me: … age?
To find your age, subtract 5 years from your age.
My age is:
16 – 5 = 11 (age)
Answer: 11 years old.
Solve problems according to the following summary:
Me: 11 years old
I’m 5 years older than you
English: … age?
To find his age, add your age to 5 years.
His age is:
11 + 5 = 16 (age)
Answer: 16 years old.
The first building has 16 floors, the second building has 4 floors less than the first building. How many floors does the second building have?
Building 1: 16 floors
Building 2 is less than building 1: 4 floors
Building 2: … floor?
To find the solution, we subtract 4 from the number of floors of the first building.
The second building has the number of floors:
16 – 4 = 12 (floor)
Answer: 12 floors.