On Monday Miriam does 5 push-ups + 7 push-ups on Tuesday = <<5+7=12>>12 push-ups on both days.
On Wednesday she does twice as many push-ups as she did on Tuesday, 7 x 2 = <<7*2=14>>14 push-ups on Wednesday.
Over the first 3 days, she did a total of 14 + 12 = <<14+12=26>>26 pushups
On Thursday Miriam did 1/2 the same number of total pushups she had already done that week, so she did 1/2 x 26 = <<1/2*26=13>>13 pushups on Thursday.
On Friday she does as many push-ups as the total of what she had done over the previous four days, so she did 5 + 7 + 14 + 13 = <<5+7+14+13=39>>39 push-ups on Friday.
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