Question

a boy runs 1 km in 12 minutes how long will he take to run 400m​

Answer 1

1 km = 1000m

∴ 1000m = 12  

 400 m = x

by cross multiplying  

1000x = 12 * 400

x = 12 * 400 / 1000

x = 12 * 4 / 10

x = 48 / 10

x = 4.8 mins

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Answer 2

1km =12min
0.4km= x

0.4*12=x

X= 4.8minutes