He ran the 10 kilometers in a total of 20 + 30 = <<20+30=50>>50 minutes.

Therefore, he ran at a pace of 50 minutes / 10 kilometers = <<50/10=5>>5 minutes per kilometer.

# Answer

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<|im_start|>system
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<|im_start|>user
TJ ran a 10K race last Saturday. He ran the first half in 20 minutes. He completed the second half in 30 minutes. What was his average time per kilometer?
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user
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TJ ran a 10K race last Saturday. He ran the first half in 20 minutes. He completed the second half in 30 minutes. What was his average time per kilometer?
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