Math Help - Writing inequality

1. Writing inequality

1. Sam must have an average of 70 or more in his summer course to obtain a grade of C. His first three test grades were 75, 63, and 68. Write a inequality representing the score that Sam must get on the last test to get a C grade.

2. The cost for a long-distance telephone call is $0.36 for the first minute and$0.21 for each additional minute or portion thereof. Write an inequality representing the number of minutes a person could talk without exceeding $3. 2. Originally Posted by Patience 1. Sam must have an average of 70 or more in his summer course to obtain a grade of C. His first three test grades were 75, 63, and 68. Write a inequality representing the score that Sam must get on the last test to get a C grade. 2. The cost for a long-distance telephone call is$0.36 for the first minute and $0.21 for each additional minute or portion thereof. Write an inequality representing the number of minutes a person could talk without exceeding$3.
1. Sam must have an average of 70 or more in his summer course to obtain a grade of C. His first three test grades were 75, 63, and 68. Write a inequality representing the score that Sam must get on the last test to get a C grade.

so you know the formula for average here would be (testscore1 + testscore2 + testscore3 + testscore4)/4

the scores for the first three are given, we have to find the last using an inequility. since we want the average to be at least 70 to get a C, we have:

Let the final score Sam needs for a C be x

then (75 + 63 + 68 + x)/4 >= 70
=> 206 + x >= 280
so x >= 74

so Sam's final score has to be at least 74 to get a C (or above) according to the above inequality.

2. The cost for a long-distance telephone call is $0.36 for the first minute and$0.21 for each additional minute or portion thereof. Write an inequality representing the number of minutes a person could talk without exceeding $3. Let x be the additional minutes we can talk for to not exceed a$3 bill. So the total number of minutes we can talk without exceeding \$3 is x+1 minutes.

we want 0.36 + 0.21x <= 3
=> 0.21x <= 2.64
=> x <=2.64/.21
=> x <= 12.57

so if y is the total number of minutes we can talk
y <= x + 1
=> y <= 13.57