Question
The average mass of a group of girls is 39 kg. If one more girl who weighs 75 kg joins the group, the new average mass of the group will become 51 kg. Find the total number of girls in the group.
3 m

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The average mass of a group of girls is 39 kg. If one more girl who weighs 75 kg joins the group, the new average mass of the group will become 51 kg. Find the total number of girls in the group.