The lowest grade that Mona can get for her last test so that her test average is 90 or more is 69.
The average is defined as the mean value of the given data which is equal to the ratio of the sum of the data value to the total number of units present in the data.
Average = the sum of the data value / the total number of units
Mona wrote 7 tests, and her test average is 93.
Average = the sum of the data value / the total number of units
where Average = 93
The total number of units = 7
The sum of the data value = 93 × 7 = 651
There will be one more test before the end of the year with a test average is 90
Similarly,
The sum of the data value = 90 × 8 = 720
The difference between these two tests gives the lowest grade that Mona can get for her last test so that her test average is 90 or more
720-651 = 69.
Thus, the lowest grade that Mona can get for her last test so that her test average is 90 or more is 69.
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