今日の暗算の結果と解答（2026/9/28）

#	My answer	Correct	Result
1	845	845	✅
2	316	316	✅
3	1,600	1,600	✅
4	147	147	✅
5	6,704	6,664	❌
6	8,603	8,603	✅
7	6,400 − 9 = 6,391	6,391	❌*
8	144	144	✅
9	27,600	23,000	❌
10	9,856	9,856	✅

I still make mistakes on simple caluculations.My mistakes are as follows.
#5: 7,000 − 48 × 7

48 × 7 = 336
7,000 − 336 = 6,664

#7: 83 × 77

Your method was perfect:

(80 + 3)(80 − 3)
= 80² − 3²
= 6,400 − 9
= 6,391

You simply wrote 6301 at the end. That’s a classic careless calculation error.

#9: 125 × 8 × 23

Here’s the shortcut:

125 × 8 = 1,000

Then:

1,000 × 23 = 23,000