The most basic method of this kind of problem is the "tick-off method" that Teacher Chen talked about at school. In addition, some concise methods are derived from this.
My view is simple: just use the basic "cross-check method" analysis and work out the answer, not much slower, the key is to be stable. Of course, it is better to master all kinds of quick and concise methods.
Multiply two numbers. If one factor increases 10 and the other factor remains the same, the product increases by 80. If one factor remains the same and the other factor increases by 6, the product increases by 72. What is an original product?
In fact, it is derived from the above "hook and fork method":
If one factor increases 10, while the other factor remains unchanged, the product increases by 80. In other words, it is "the constant factor of 10 times is the product increment of 80 times", so the formula of 1 is:
80 ? 10 = 8
Similarly: "6 times of other factors is 72 times of product increase", so other factors are:
72 ? 6 = 12
The original product is:
12 8 = 96
This is essentially the same as the "hook and fork method".
The sum of the two addends is 13 1. Obviously, the 0 in each digit of one of the addends is omitted in the calculation, and the calculated sum is 77. Find these two addends.
So one number is 60 and the other addend is 13 1-60 = 7 1.
That is to deepen understanding: if a 0 is omitted, the original number of ten digits will reach single digits, which is actually reduced by (10- 1 = 9) times; (The 10th place is 10, and you are all 1 0, so you have reduced it by 9 times). This leads to and reduces 13 1-77 = 54.
So, the ten digits that missed the plus number 0 are 54? 9 = 6; So this addend is 6 10 = 60.
Xiaohong mistook dividend 268 for 286 when calculating a division with remainder. The result quotient is 1 and the remainder is 6. What is the correct division formula?
Correct division formula: 268? 12 = 22 ... four
See more dividends: 286-268 = 18.
The quotient is 1, which means that there is one more divisor and the remainder is 6, so the dividend is18; therefore
Divider: 18-6 = 12.
Division formula: 268? 12 = 22 ... four
3230 - 2890 = 340
Why is it 340 more? Because there are four other multipliers between 4 and 8;
So, another correct multiplier is:
8 - 4 = 4
340 ? 4 = 85
2890 ? 85 = 34 === The ten digits of the wrong multiplier are 3, so the wrong multiplier should be 36;
Correct product: 85 36 = 3060
A and B are calculating an addition problem of three digits plus two digits. The result of A calculation is 258, and B mistakenly adds the number on the hundredth digit of three digits with the number on the tens digit of two digits, and adds the number on the tenth digit of three digits with the number on the tens digit of two digits, and the calculated answer is 645. What are two addends?
Why is the score of 645-258 = 387 // B 387 higher than that of A?
10- 1 = 9 // B Add a 0 after the two-digit number, which is equivalent to 9 times of the two-digit number.
387 ? 9 = 43 // two digits
258-43 = 2 15 // three digits
You can also calculate three digits: 645-430 = 2 15.