Operations with decimal numbers are present in our daily activities from the time we wake up to go to school. The hours, the price of lunch, the amount of money you take to school, the value of fuel at the gas station and even the grade you got on the test are represented by decimal numbers. Knowing how to perform operations with these numbers is very important to solve daily problems that appear in our lives.
Let's see how to proceed with the multiplication of decimal numbers. We have two cases:
1. Multiplication of a decimal number by a natural number.
Example 1. Sabrina bought four chocolates for R$1.75 each. How much did Sabrina spend?
Solution: If each chocolate cost R$1.75, let's use the multiplication algorithm to determine the total value of Sabrina's purchase.
Answer: Sabrina spent R$7.00.
Note that the number of decimal places present in the final result is the same.
2. Decimal by decimal multiplication.
Example 2. Dona Maria went to the supermarket and bought 1.5 kg of meat. If a kilo of meat was costing R$ 7, 80, how much was Dona Maria's purchase?
Solution: The operation to be performed is multiplication. Thus, we will have:
Note that the number of decimal places in the answer is the sum of the number of decimal places of the two numbers that were multiplied. When zero is the last digit of the decimal part, it has no value, so 11.700 = 11.70.
Answer: The purchase of Dona Maria was R$ 11.70.
Important notes: When multiplying decimal by natural, the number of decimal places in the answer is the same as the number that was multiplied.
When we multiply decimal by decimal, the number of decimal places in the answer is the sum of the decimal places of the two numbers that were multiplied.
Now do it yourself.
Perform the indicated multiplications:
a) 3.25 x 19 =
b) 6.8 x 10 =
c) 1.43 x 6.4 =
d) 7.9 x 2.7 =
e) 3.4 x 3.99 =
f) 6.1 x 8.5 =
g) 121 x 7, 4=
By Marcelo Rigonatto
Mathematical
Take the opportunity to check out our video lesson on the subject:
