How old is Jack?

$\text{Let Bao be}$ $x$ $\text{so Jack is}$ $x+13$ $\text{years old.}$ $\text{Now after 8 years,in accordance with the problem,we get an equation}$ : $2(x+8)=x+13+8 \\ \Rightarrow{2x+16=x+21} \\ \Rightarrow{x=5}$ $\text{So Bao is 5 years old and jack is 18 years old}.$

Trick question! If he is 13 years older than Bao then to be double his age he would need to be 26 but that is 8 years later so simply 26-8=18 is the answer.

Jack is 13 years older than Bao, J=B+13 or J-13=B

In 8 years, he will be twice as old as Bao, (J+8)=2(B+8)

How old is Jack now? J+8 = 2(J-13+8) or J=18

$B=J-13$ $\color{#D61F06}(1)$

$J+8=2(B+8)$ $\color{#D61F06}(2)$

Substitute $\color{#D61F06}(1)$ in $\color{#D61F06}(2)$ .

$J+8=2(J-13+8)$

$J+8=2(J-5)$

$J+8=2J-10$

$8+10=J$

$\boxed{18=J}$

let Bao be x year old , according to question x+13+8=2(x+8), x+21=2x+16, x=5. So Bao is 5 years old now and Jack is 18 years.

let as assume J a Jack and B as Bao J=13+B. We know also that J=2B+8 . B=J-13 IF we substitute the value of B TO J-13 We have J=2(J-13)+8 J=2J-26+8 2J-J=26-8 J=18 WE KNOW THAT B=J-13 B= 18-13=5

Even if you're clueless, just try each answer choice to see if it fits the problem statement. Otherwise, take any approach already shown in the other responses.