Equations to solve problems

Question

A track star ran the 100-meter event in six track meets. Her average time for all six meets was 11.8 seconds. She could not find the record for her running time in the last meet, but she had all the other ones: 11.5 seconds, 11.8 seconds, 11 seconds, 12.3 seconds, 11.3 seconds, what was her running time for her last meet?

Answer 1

Average = total/count

Average * count = total

11.8 * 6 = 11.5 + 11.8 + 11 + 12.3 + 11.3 + X

70.8 = 57.9 + X

x = 70.8 - 57.9

= 12.9