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.
That is really easy to do in your head :)
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....!!! }
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.
That is really easy to do in your head :)