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Guest Mar 26, 2015

#2
+92206
+5

I could do that in my head Chris but then I am a show off.  LOL

Here is another easier way and it works for all numbers ending in 5

25^2=2^2+2 then add 25 = 625

75^2 = 7^2+7 then add 25 = 5625

35^2=3^3+3 then add 25 = 1225

105^2=10^2+10 then add 25 = 11025

etc.

Melody  Mar 26, 2015
Sort:

#1
+85675
+5

I always think of things like that in this way :

(20 + 5) (20 + 5)

I see that multiplying the first two terms gives me 400

Then, I have 5 x 20,  twice  = 200

Finally, the last two terms multiplied together = 25

So..adding the results, we have......400 + 200 + 25 = 625

{However....since I just did this on "paper".....I guess it wasn't done in my head after all....!!! }

CPhill  Mar 26, 2015
#2
+92206
+5

I could do that in my head Chris but then I am a show off.  LOL

Here is another easier way and it works for all numbers ending in 5

25^2=2^2+2 then add 25 = 625

75^2 = 7^2+7 then add 25 = 5625

35^2=3^3+3 then add 25 = 1225

105^2=10^2+10 then add 25 = 11025

etc.