#5**+10 **

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

Brodudedoodebrodude
May 27, 2015

#2**+5 **

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)

geno3141
May 26, 2015

#5**+10 **

Best Answer

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

Brodudedoodebrodude
May 27, 2015