Question 478304
Tom's home is 1,800 m from his school. One morning he walked part of the way to school and then ran the rest. If it took him 20 minutes or less to get school, and he walks at 70m/min. and runs 210m/min how far did he run?
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let x=meters Tom ran
1800-x=meters Tom walked
Travel time=distance/speed
x/210+(1800-x)/70=20
LCD=210
x+3(1800-x)=4200
x+5400-3x=4200
-2x=-1200
x=600 
ans:
Tom ran for 600 m