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GeneralRe: Mental arithmetic Pin
PIEBALDconsult17-Aug-20 7:53
mvePIEBALDconsult17-Aug-20 7:53 
GeneralRe: Mental arithmetic Pin
W Balboos, GHB17-Aug-20 7:56
W Balboos, GHB17-Aug-20 7:56 
GeneralRe: Mental arithmetic Pin
MarkTJohnson17-Aug-20 8:25
professionalMarkTJohnson17-Aug-20 8:25 
GeneralRe: Mental arithmetic Pin
Jörgen Andersson17-Aug-20 9:56
professionalJörgen Andersson17-Aug-20 9:56 
GeneralRe: Mental arithmetic Pin
James McCullough17-Aug-20 11:40
professionalJames McCullough17-Aug-20 11:40 
GeneralRe: Mental arithmetic Pin
Frank Malcolm17-Aug-20 21:36
Frank Malcolm17-Aug-20 21:36 
GeneralRe: Mental arithmetic Pin
Davyd McColl17-Aug-20 21:57
Davyd McColl17-Aug-20 21:57 
GeneralRe: Mental arithmetic Pin
jsc4217-Aug-20 23:34
professionaljsc4217-Aug-20 23:34 
Everyone should know the squares - at least for 1 to 20. After that, you just need to know that multiples of ten are (x * 10)^2 = x^2 * 100. You can then do the halfways [numbers ending in 5] (x * 10 + 5)^2 = ((2x + 1) * 10)^2 / 4 [looks a lot more complicated than it is]; thereafter, for numbers ending in 1, 2, 6, 7 you apply (x + 1)^2 = x^2 + 2x + 1 (or x^2 + (x + 1) + x) [do it twice for 2 and 7] and for numbers ending in 3, 4, 8, 9 you apply (x - 1)^2 = x^2 - 2x -=1 or x^2 - (x + 1) - x = x^2 - x - x - 1 [do it twice for 3 and 8]

At least, that's what I use! And I assure you, once you've got the hang of them that are simple.

Edit: It is also useful to memories powers of two and squares of prime numbers

modified 18-Aug-20 6:03am.

GeneralRe: Mental arithmetic Pin
W Balboos, GHB18-Aug-20 1:36
W Balboos, GHB18-Aug-20 1:36 
GeneralRe: Mental arithmetic Pin
Rick York17-Aug-20 8:02
mveRick York17-Aug-20 8:02 
GeneralRe: Mental arithmetic Pin
Jörgen Andersson17-Aug-20 8:05
professionalJörgen Andersson17-Aug-20 8:05 
GeneralRe: Mental arithmetic Pin
OriginalGriff17-Aug-20 8:08
mveOriginalGriff17-Aug-20 8:08 
GeneralRe: Mental arithmetic Pin
pkfox17-Aug-20 8:51
professionalpkfox17-Aug-20 8:51 
GeneralRe: Mental arithmetic Pin
Jon McKee17-Aug-20 9:23
professionalJon McKee17-Aug-20 9:23 
GeneralRe: Mental arithmetic Pin
Nelek17-Aug-20 19:44
protectorNelek17-Aug-20 19:44 
GeneralRe: Mental arithmetic Pin
kmoorevs17-Aug-20 10:32
kmoorevs17-Aug-20 10:32 
GeneralRe: Mental arithmetic Pin
Joop Eggen17-Aug-20 20:25
Joop Eggen17-Aug-20 20:25 
GeneralRe: Mental arithmetic Pin
Jörgen Andersson17-Aug-20 20:27
professionalJörgen Andersson17-Aug-20 20:27 
GeneralRe: Mental arithmetic Pin
Joop Eggen17-Aug-20 20:45
Joop Eggen17-Aug-20 20:45 
GeneralRe: Mental arithmetic Pin
bjongejan18-Aug-20 0:50
bjongejan18-Aug-20 0:50 
PraiseRe: Mental arithmetic Pin
Joop Eggen18-Aug-20 2:23
Joop Eggen18-Aug-20 2:23 
GeneralRe: Mental arithmetic Pin
englebart18-Aug-20 2:54
professionalenglebart18-Aug-20 2:54 
GeneralRe: Mental arithmetic Pin
Caslen17-Aug-20 20:32
Caslen17-Aug-20 20:32 
GeneralRe: Mental arithmetic Pin
aserrano17-Aug-20 20:34
aserrano17-Aug-20 20:34 
GeneralRe: Mental arithmetic Pin
Jörgen Andersson17-Aug-20 20:39
professionalJörgen Andersson17-Aug-20 20:39 

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