Chapter 3 - Section 3-3 - Cumulative Distribution Functions - Exercises - Page 73: 3-47

$F(x)=\left\{\begin{array}{ll}{0,} & {X<10} \\ {0.2,} & {10 \leq X<25} \\ {0.5,} & {25 \leq X<50} \\ {1,} & {X \geq 50}\end{array}\right.$

Since, $f(x)=\left\{\begin{array}{ll} {0.2,} & {X=10} \\ {0.3,} & {X=25} \\ {0.5,} & {X = 50}\end{array}\right.$ then, $F(x)=\left\{\begin{array}{ll}{0,} & {X<10} \\ {0.2,} & {10 \leq X<25} \\ {0.2+0.3=0.5,} & {25 \leq X<50} \\ {1,} & {X \geq 50}\end{array}\right.$