30x2=60 (days)

60÷2=30 (which means there are 30 2 days in 60).

30x3=90 (liter)

90÷ 18=5 (barrel)

A: Xiaoming's family drinks about 5 barrels of water every two months.

analyse

This topic examines the application of four operations.

Two months is 60 days, and 60 days has 30 2 days, so you need to drink 30 3 liters of water. That's 90 liters. There are 5 18 liters in 90 liters, which means drinking 5 barrels of water.

Four algorithms:

1, integer multiplication rule:

Starting from the right, multiply the first factor by the number on each bit of the second factor in turn, and the end of the number will be aligned with which bit of the second factor; Then add up the numbers multiplied by several times.

2. Decimal multiplication rule:

Calculate the product according to the law of integer multiplication; Look at how many decimal places a factor * * * has. Just count the decimal places from the right of the number and point to the decimal point. There is a 0 at the end of the decimal part of the number, so it is generally necessary to remove the 0 and simplify it.

3, fractional multiplication rule:

Multiply the numerator of each fraction as the numerator, multiply the denominator of each fraction as the denominator, and then reduce the fraction.

4, integer division rule

Start with the high order of the dividend, first look at how many digits there are in the dividend, and then try to divide the first few digits of the dividend by the divisor. If it is less than the dividend, try dividing it by one digit. Write the quotient on it except the dividend; The remainder after each division operation must be less than the divisor.

5, the divisor is an integer fractional division rules:

According to the law of integer division, the decimal point of quotient should be aligned with the decimal point of dividend; If there is a remainder at the end of the dividend, fill in zero after the remainder and continue the division.

6, divisor is a decimal division rule:

To calculate the divisor is the division of decimal, first move the decimal point of the divisor to make it an integer; The decimal point of the divisor is shifted to the right by several digits, and the decimal point of the dividend is also shifted to the right by several digits (the digits are not enough, and the end of the dividend is supplemented by "0"); Then it is calculated according to the division rule that the divisor is an integer.

Extended data:

A clever way to apply problems:

First, the application problem needs to transform the text description in the topic into a mathematical formula; Second, in the face of a lot of text information in the topic, children often can't grasp where the key information is; Third, the child just started to contact the application problem, did not develop the good habit of doing the problem, did not pay attention to what the question asked, and began to write and do, often in the opposite direction; Fourth, children don't pay attention to writing habits, don't bring units, don't answer, don't check, and often lose points in exams.