Question 955551

If {{{s }}}is the amount of time it takes Joe to solve a puzzle and 
{{{d }}}is the amount of time it takes his friend Bob to design the puzzle, 
then which of the following equations best fits the information in the table above? 

{{{d}}}|{{{s}}}
{{{1}}}|{{{5}}}  
{{{2}}}|{{{7}}}
{{{3}}}|{{{9}}}
{{{4}}}|{{{11}}}
{{{5}}}|{{{13}}}

since this is a linear function we can find equation {{{s=md+b}}} first:
find a slope: {{{(7-5)/(2-1)=2}}}; so our option is {{{2d}}} 
now use one point and slope to find {{{b}}}, 
{{{9=2*3+b}}}
{{{9-6=b}}}
{{{b=3}}}

so, our equation is {{{s=2d+3}}}
check:
{{{d}}}|{{{s}}}
{{{1}}}|{{{5}}} =>{{{2*1+3=5  }}}
{{{2}}}|{{{7}}}=>{{{2*2+3 =7 }}}
{{{3}}}|{{{9}}}=>{{{2*3+3 =9 }}}
{{{4}}}|{{{11}}}=>{{{2*4+3  =11}}}
{{{5}}}|{{{13}}}=>{{{2*5+3  =13}}}