心算 - 两个十几之数互成

in cn •  3 years ago 

image.png

原理公式如下
17 X 14
= 17 X 10 + ( 10 + 7 ) X 4
= 17 X 10 + 10 X 4 + 7 X 4
= ( 17 + 4 ) X10 + 7 X 4
= 210 + 28
= 238

從公式中發現到
10 的數共有 (17+4) 個
個位數為 7 X 4
所以我們先把17+4=21記住為210
再去加上 28
便算出結果 238

Authors get paid when people like you upvote their post.
If you enjoyed what you read here, create your account today and start earning FREE BLURT!