model subtraction of fraction:

jeffrey has already run 3/8 of the race. What fraction of the race does Jeffrey have left? Write and solve the equation

The entire race is 1 full race.

One full race is 1.

He ran 3/8 of 1, so he ran 3/8.

He needs to run the rest of the race.

The rest is unknown, so we call it x.

When you add 3/8 to the unknown, you get the full race.

The equation is

x + 3/8 = 1

Change 1 to a denominator of 8.

x + 3/8 = 8/8

Subtract 3/8 from both sides.

x = 5/8

Answer: He still needs to run 5/8 of the race.