19 is only 1 away from 20, so you prefer to start by multiplying 20 times 5, which equals 100. Then we need to take away a squadron of 5, because there are actually only 19 squadrons, not 20. 100 take ...

To multiply two numbers with the same unit places, such as 97 and 98, one can write it as (100-3) x (100-2). Next, add the two numbers 3 and 2 together, which gives 5. Subtract 5 from 100 (as it falls ...

Is There a Way to Square 2-Digit Numbers Quickly? While it’s easy to calculate the squares of single-digit numbers like 5 in your head (since those squares are part ...

This summer, battle lines were drawn over a simple math problem: 8 ÷ 2(2 + 2) = ? If you divide 8 by 2 first, you get 16, but if you multiply 2 by (2 + 2) first, you get 1. So, which answer is right?

こんにちは！「100日後にそろばん完全マスター！」の主です。 Youtube37日目の動画「暗算6級 2桁×1桁のかけ暗算」の内容を簡単に解説します。 第二章のそろばん10.9級編のかけ算のやり方をマスターしていれば、2桁×1桁のかけ暗算の計算もスムーズにできる ...