Categories

## Average – AMC 10B – 2019 – Problem No – 4

Let’s try this problem based on average from AMC 10B, 2019.

Mr. Patrick teaches math to 15  students. He was grading tests and found that when he graded everyone’s test except Payton’s, the average grade for the class was 80 . After he graded Payton’s test, the test average became 81. What was Payton’s score on the test?

• 81
• 95
• 85
• 91

### Key Concepts

Average

Mean

Arithmetic

AMC 10A – 2015 – Problem No – 5

Challenges and Thrills in Pre-College Mathematics

## Try with Hints

If you are not getting correct answer you can start from here :

The average of a set of numbers is the value we get if we evenly distribute the total across all entries. So assume that the first  14 students each scored  80.

If Payton also scored an 80 the average would still be 80. In order to increase the overall average to 81 we need to add one more point to all of the scores, including Payton’s. This means we need to add a total of  15 more points, so Payton needs 80+15 = 95 .

Categories

## What is Average ?

In mathematics and statistics, average refers to the sum of a group of values divided by n, where n is the number of values in the group. An average is also known as a mean.

## Try this sum from AMC 10 – 2020

Driving along a highway, Megan noticed that her odometer showed 15951 (miles). This number is a palindrome-it reads the same forward and backward. Then 2 hours later , the odometer displayed the next higher palindrome. What was her average speed, in miles per hour, during this 2 – hour period ?

A) 50 B) 55 C)60 D) 65 E) 70

American Mathematics Competition 10 (AMC 10B), {2020}, {Problem Number 6}

Average

4 out of 10

Mathematics can be fun

## Use some hints

Do you really need any hint ???

Try this out:

In order to get the smallest palindrome greater than 15951 , we need to raise the middle digit. If we were to raise any of the digits after the middle, we would be forced to also raise a digit before the middle to keep it a palindrome, making it unnecessarily larger.

So what can we do here ?

We can raise 9 to the next largest value, 10 , but obviously, that’s not how place value works, so we’re in the 16000 s now . To keep this a palindrome, our number is now 16061.

If you really need the final hint this can be the life saver for this sum :

So Megan drove 16061 – 15951 = 110 miles . Since this happened over 2 hours , she drove at $\frac {110}{2}$ = 55 mph .