Tìm số trung bình cộng của mỗi nhóm số sau đây:

a) 87, 13 và 50 ......................................................... ......................................................... .........................................................	b) 9 712, 288, 513 và 87 ......................................................... ......................................................... .........................................................
c) 12, 38, 90, 75 và 25 ......................................................... ......................................................... .........................................................	d) 2 739, 1 372, 620, 719, 82 và 12 ......................................................... ......................................................... .........................................................

a) 325 +  264 + 175 + 436

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b) 2 500 + 1 800 + 4 500 + 1 200

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c) 1 035 + 2 568 + 4 065 + 2 432

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d) 7 670 + 3 728 + 2 330 + 1272

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a) 726 528 + 121 637

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b) 862 127 – 472 812

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c) 276 257 – 212 982

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d) 272 782 + 527 182

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e) 638 318 – 371 673

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f) 128 748 + 247 837

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