Point D is between points C and F as the diagram shows. Without using a visual aid, you can tell based on how CD and DF are ordered. Note how the "D"s in CD and DF are adjacent when you place them together
CD DF ---> CF
That is one way to think about it. Although, for me, a visual guide is better.
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Point C is at location 20 on the number line. We move 3 spots over to get to point D, so D is at 20+3 = 23 on the number line. Then we move another 5 units to the right to get to point F which is at 23+5 = 28
C = 20
D = 23
F = 28
