A runner is compared with the world record holder during a race. A negative number means the runner is ahead of the time of the world record holder. A positive number means the runner is behind the time of world record holder. The table shows the time difference between the runner and the world record holder for each lap. What time difference does the runner need for the 4th lap to match world record? Lap 1 time difference is -1.23, lap 2 time difference is 0.45, lap 3 time difference 0.18. Lap 4 is unknowns
we have that
Lap 1 =-1.23
Lap 2=0.45
Lap 3=0.18
Lap 4=x
Adds the times
-1.23+0.45+0.18+x
-0.60+x
equate to zero
-0.60+x=0
x=0.60
therefore
the time in Lap 4 must be 0.60 to to match world record