Solving Math textbook exercises 5 Lessons: Practice
1. Solve problem 1 page 165 Math textbook 5
Find the percentage of:
a) \(2 \,\, \text{and} \,\, 5\) b) \(2 \,\, \text{and} \,\, 3\)
c) \(3,2 \,\, \text{and} \,\, 4\) d) \(7.2 \,\, \text{and} \,\, 3,2\)
Attention: If the percentage is a decimal, use only two digits in the decimal.
Example: \(1 : 6 = 0.166666…\)
The percentage of \(1\) and \(6\) is: \(16,66\%\)
Solution method
To calculate the percentage of two numbers, we take the first number divided by the second number, then multiply that quotient by \(100\) and then add the symbol \(\%\) to the right of the result.
Solution guide
a) The percentage of \(2 \,\, \text{and} \,\, 5\) is:
\(2 : 5 \times 100 = 40\%\)
b) The percentage of \(2 \,\, \text{and} \,\, 3\) is:
\(2 : 3 \times 100 = 66.66\%\)
c) The percentage of \(3,2 \,\, \text{and} \,\, 4\) is:
\(3,2 : 4 \times 100 = 80\%\)
d) The percentage of \(7.2 \,\, \text{and} \,\, 3.2\) is:
\(7.2 : 3.2 \times 100 = 225\%\)
2. Solve problem 2 page 165 Math textbook 5
Calculate:
a) \(2,5\% + 10.34\%\)
b) \(56.9\% – 34.25\%\)
c) \(100\% – 23\% – 47.5\%\)
Solution method
Apply the formulas:
\(A\% + B\% = (A + B)\%\)
\(A\% – B\% = (A – B)\%\)
Solution guide
a) \(2,5\% + 10.34\% = 5.9\%\)
b) \(56.9\% – 34.25\% = 22.65\%\)
c) \(100\% – 23\% – 47.5\% = 77% – 47.5% = 29.5%\)
3. Solve problems 3 pages 165 Math textbook 5
One district has \(320\) hectares of land for coffee trees and \(480\) hectares of land for rubber trees. Ask:
a) What is the percentage of land planted with rubber trees?
b) What is the percentage of land planted with coffee trees?
Solution method
a) Divide the area under rubber plantations by \(100\) and then add the symbol \(\%\) to the result.
b) Take the coffee growing area, divide the rubber plantation area by \(100\) and then add the symbol \(\%\) to the result
Solution guide
a) Percentage of rubber growing area compared to coffee growing area is:
\(480 : 320 \times 100 = 150\%\)
b) Percentage of coffee growing area compared to rubber area is:
\(320 : 480 \times 100 = 66.66\%\)
Answer:
a) \(150\%\)
b) \(66,66\%\)
4. Solve problems 4 pages 165 Math textbook 5
Class 5A intends to plant \(180\) trees, so far has planted \(45\%\) number of trees. According to the plan, how many more trees will class 5A have to plant?
Solution method
– Calculate the number of planted trees = the number of trees to be planted: 100 × 45
– Number of trees to be planted = number of trees to be planted – number of trees planted.
Solution guide
The number of planted trees in class 5A is:
\(180 \times 45 : 100 = 81\) (tree)
The number of trees of class 5A that still need to be planted to complete the plan are:
\(180 – 81 = 99\) (tree)
Answer: \(99\) tree
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