The estimation method of addition and subtraction in the third grade of primary school is greater than 5 and less than 5. It can also be understood as four families with five mouths: 0, 1, 2, 3, 4, all without carry; Five, six, seven, eight, nine. For example:

Xiaoming's mother went to the mall to buy vinegar and soy sauce. The price of vinegar is 17 yuan and the price of soy sauce is 12 yuan. Estimate how much money Xiao Ming's mother needs to bring.

This should be estimated as follows: 17≈ 20,12 ≈10,20+10 = 30 (yuan).

A: Xiaoming's mother needs to bring 30 yuan money.

Extended data:

A 50% pair of four families and six families has always been used as an accurate counting reservation method. Here "four" means less than five, "six" means more than five, and "five" means the rounded mantissa. When the mantissa meets five, just look at the front, and even the odd ones can't get in.

For example, 1.25 keeps one decimal place, because 2 is an even number, so it is 1.2. Another example is 1.35, because 3 is an odd number, it is 1.4.

From the statistical point of view, "four families, six families and 50% pairs" is more scientific than "rounding", which makes the rounding result bigger, smaller and more uniform. Instead of entering it every Friday like rounding, the result is biased towards large numbers.

For example:1.15+1.25+1.35+1.45 = 5.2. If one decimal place is rounded, the calculation is as follows:

1.2+ 1.3+ 1.4+ 1.5=5.4

According to the calculation of "four houses in six and fifty pairs",1.2+1.2+1.4+0.4 = 5.2, the rounding result can better reflect the actual result.