debra is participating in a 5 day cross country biking challenge. she biked for 61, 52, 68 and 45 miles on the first four days how many miles does she need to bike on the last day so that her average (mean) is 56 miles per day?

(61 + 52 + 68 + 45 + x)/5 = 56 (add all of the miles for the first 4 days, x is the number of miles on the 5th day)

(226 + x)/5 = 56 (since we want the average, we want to add 5 days mileage divided by 5 to get an average of 56 miles per day.

Multiply 5 both sides

5 * (226+x)/ = 56 * 5

226+x = 280

Now subtract 226 from 280 to solve for x.

x + 226 - 226 = 280 - 226

x = 54 miles on the 5th day

To check:

(61 + 52 + 68 + 45 + 54)/5 = 56

280/5 = 56 CHECKS OUT!

One small error, on the line following Multiply 5 both sides, it should read

5 * (226 + x)/5 = 56 * 5 (this is to get rid of the 5 in the denominator on the left hand side)

226+x = 280 (after multiplication is done).

Sorry about the error. Let me know if you have any questions.

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