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Answer: 56 minutes
Using words
walk, run takes 40 minutes
run, run takes 24 minutes
running takes 12 minutes each way
walk, run takes 40 minutes total, 12 come from running on the way back
So the walking must take 28 minutes.
walk, walk takes 28$\times$2 = 56 minutes.
Using algebra
If it takes John $w$ minutes to walk to (or from) school and $r$ minutes to run to (or from) school, then we have $$\begin{align}r+w&=40\\2r&=24\\2w&=?\end{align}$$
Finding $r$ first
$2r=24\Rightarrow r=12.$ Substituting this into $r+w=40$ gives $12+w=40\Rightarrow w=28.$ So $2w=2\times28=56.$ So it takes $56$ minutes to walk both ways.
Doubling the first equation
Doubling both sides of $r+w=40$ gives $2r+2w=80.$ Since $2r=24,$ $24+2w=80\Rightarrow 2w=80-24=56.$ So it takes $56$ minutes to walk both ways.
Walk or Run?
Age 11 to 14
ShortChallenge Level 
Answer: 56 minutes
Using words
walk, run takes 40 minutes
run, run takes 24 minutes
running takes 12 minutes each way
walk, run takes 40 minutes total, 12 come from running on the way back
So the walking must take 28 minutes.
walk, walk takes 28$\times$2 = 56 minutes.
Using algebra
If it takes John $w$ minutes to walk to (or from) school and $r$ minutes to run to (or from) school, then we have $$\begin{align}r+w&=40\\2r&=24\\2w&=?\end{align}$$
Finding $r$ first
$2r=24\Rightarrow r=12.$ Substituting this into $r+w=40$ gives $12+w=40\Rightarrow w=28.$ So $2w=2\times28=56.$ So it takes $56$ minutes to walk both ways.
Doubling the first equation
Doubling both sides of $r+w=40$ gives $2r+2w=80.$ Since $2r=24,$ $24+2w=80\Rightarrow 2w=80-24=56.$ So it takes $56$ minutes to walk both ways.
You can find more short problems, arranged by curriculum topic, in our short problems collection.
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