Problem solving question help...

A students scores on the first three tests in a math course are 65,75 and 87. What range of scores on a fourth test will give the student an average that is less than 80 but no less than 70 for the four tests?

65+75+87+x/4 < 79.9, x<92.6

65+75+87+x/4 >(and equal to) 70, x>(and equal to) 53

So the range of scores would be 53 to 92.6? Is this correct and am I writing this down correctly?

Thank you very much

Re: Problem solving question help...

now for the conditions you have stated, the inequalities are:

where x is the marks in the fourth subject.

and and (after solving the two inequalities).

therefore the range of marks to satisfy the stated condition are , the open interval from 53 to 93,i.e every number possible between 53 and 93 but without 53 and 93 itself.

Re: Problem solving question help...

Re: Problem solving question help...

Except 65 + 75 + 87 = 227, not 230.

Re: Problem solving question help...

Thank you so much you guys!