Multiplying a two-digit number ending in 1 times another two-digit number ending in 1

 

Ex.1  41 x 5 1 =____    Ex.2  21 x 5 1 =____    Ex.3  81 x 91 =____

 

Multiply the tens digits for the first digits in the answer.

Ex.1  41 x 51 = 20__    Ex.2  21 x 51 = 10__    Ex.3  81 x 91 = 72__

 

Add the tens digits for the tens digits of the answer. *There may be a carry figure, never more than one.

Ex.1  41 x 51 = 209_    Ex.2  21 x 51 =107_   *Ex.3  81 x91 = 737_

1 is the ones digit of the answer.

Ex.1  41 x 51 = 2091    Ex.2  21 x 51 = 1071    Ex.3  81 x 91 = 7371

 

Try these:  a) 31 x 81 =    b) 51 x 61 =    c) 71 x 91 =

Author: David

I grew up near Clayton, AL and have lived over 30 years near Atlanta, GA. My interests include family, church, guitar, gardening, working with kids... and math! Life can be very interesting. My websites: chasingtrees.net mathshortcutblog.wordpress.com

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