How to write these two questions, primary school math report, fifth grade thinking solution.

The correct calculation method of (5+□)×2.4 is: 5×2.4+□×2.4, while Ma Xiaohu calculated: 5+□×2.4.

It can be seen that "5" in Ma Xiaohu's formula is added without multiplying 2.4, that is, 2.4- 1= 1.4 is added less, that is, 1.4×5=7 is added less.

Only the last digit of Ma Xiaohu's answer is wrong, so the sum of seven natural numbers must be greater than 10.4×7=72.8.

The sum of seven natural numbers must also be a natural number.

If the total is 73, the average value is 10.43.

If the total is 74, the average value is 10.57.

The average of seven numbers must be between 10.4 and 10.5, so the average of these seven natural numbers can only be 10.43.

So Ma Xiaohu should write 10.43 as 10.42, and he forgot to round it off.