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if were only allowed to use >>, -, + to make a number X times the constant K lets assume K is 17 and K is 20 how to make an expression for each

I was trying to think of ways to do this but I cant.

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Could you elaborate? Operating only on $K$ itself you cannot make it larger by merely right-shifting, assuming you do not carry over bits shifted right-out. What is $1>>1$? How are $+, -$ defined? What can they operate on? –  gnometorule Dec 18 '12 at 18:01
    
I got the answer look at it below that looks right –  jyuserersh Dec 18 '12 at 18:13

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If $a$ is expressed in binary $$2^n\cdot a=a<<n$$ where $<<$ is the bitwise left shift operator.

$$17\cdot a=(2^4+1)\cdot a=(a<<4)+a$$ and $$20\cdot a=(2^4+2^2)\cdot a=(a<<4)+(a<<2)$$

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