6. John always walks to and from school at the same speed. When he walks to school along the road and walks back using a short cut across the fields, he walks for 50 minutes. When he uses the short cut both ways, he walks for 30 minutes. How long does it take him when he walks along the road both ways?
A 60 minutes
B 65 minutes
C 70 minutes
D 75 minutes
E 80 minutes
Solution
C

Since using the short cut both ways takes 30 minutes, using the short cut one way takes 15 minutes. Hence, since walking to school by road and walking back using the short cut takes 50 minutes, walking by road takes $(50-15)$ minutes $=35$ minutes. Therefore walking by road both ways takes $2 \times 35$ minutes $=70$ minutes.