What is 17 * 24. No Calculator!

Here's the Exact process I followed to solve it in my head:

Split it up into 2 parts, 17*20 + 17* 4

First work out 17*4 in my head and remember it -> 10*4 + 7*4 = 40+28 = 68

Now 17*20 is 17*10*2 = 340.

Now I just add up these two numbers -> 340 + 68 = 408

it is 408...

If you can multiply by 2 and keep some numbers in mind, you can do it without a calculator and without writing anything down but the final answer.

17 x 2  =  34

17 x 4  =  17 x (2 x 2)  =  (17 x 2) x 2  =  34 x 2  =  68 

17 x 20  =  (17 x 2) x 10  =  34 x 10  =  340

If you can keep those two answers in mind, ading 340 and 68 gives you 408.

(340 + 68  =  340 + 60 + 8  =  408)

17 * 24  =

34 * 12  =

68 * 6 =

60*6  + 8*6  =   360 + 48  = 408

(20 - 3)*(20 + 4) = 20^2 +20*4 - 20*3 - 3*4 = 400 + 20 - 12 = 408

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I use Brodude'smethod.

It seems to be simple and easy.