math homework help!!!!!!!!!!!!!!!!!!!!!!!!!!?

easiest way is to assume the 21 is the median, then the 7th test grade should be higher or equal to 21.

21 x 7 = 147

147 - 17 -19 -1 20 - 21 - 24- 25 = 21.

in this case, 17, 19, 20, 21, 24, 25, 21, mode median average are equal to 21

in another way, if you assume the median is

20, then the 7th grade is lower or equal to 17

20 x 7 = 140,

140 - 126 = 14,

so the grades will be 17, 19, 20, 21, 24, 25, 14, median and average are both 20 but mode is not 20.

so 17, 19, 20, 21, 24, 25, 21 is the only solution.

you have to show both possibilities and prove only one solution to get full mark

It's 21. The median could have only been one of 2 answers, either 20 or 21 depending on where the girls next score would have been ranked. So all you had to do was test either of those to get the correct answer.

Mode = Median = average = 21 if 7th score = 21. ///