13 Use the associative property to complete the following. a \( (3+7)+15=3+(7+15)=\square+\square=\square \) b \( 20+(9+21)=(20+9)+21=\square+\square=\square \) c \( (2 \times 16) \times 10=2 \times(16 \times 10)=\square \times \square=\square \) d \( 5 \times(3 \times 150)=(5 \times 3) \times 150=\square \times \square=\square \)

To complete the problems using the associative property, we will follow the steps of evaluating the expressions and filling in the squares with the appropriate values. ### a Given: \[ (3+7)+15=3+(7+15) \] 1. Calculate \(3 + 7\): \[ 3 + 7 = 10 \] 2. Now substitute back: \[ (10) + 15 = 10 + 15 = 25 \] 3. Calculate \(7 + 15\): \[ 7 + 15 = 22 \] 4. Now substitute back: \[ 3 + (22) = 3 + 22 = 25 \] Thus, we can fill in the squares: \[ \text{a: } 10 + 15 = 25 \] ### b Given: \[ 20+(9+21)=(20+9)+21 \] 1. Calculate \(9 + 21\): \[ 9 + 21 = 30 \] 2. Now substitute back: \[ 20 + (30) = 20 + 30 = 50 \] 3. Calculate \(20 + 9\): \[ 20 + 9 = 29 \] 4. Now substitute back: \[ (29) + 21 = 29 + 21 = 50 \] Thus, we can fill in the squares: \[ \text{b: } 20 + 30 = 50 \] ### c Given: \[ (2 \times 16) \times 10 = 2 \times (16 \times 10) \] 1. Calculate \(2 \times 16\): \[ 2 \times 16 = 32 \] 2. Now substitute back: \[ (32) \times 10 = 32 \times 10 = 320 \] 3. Calculate \(16 \times 10\): \[ 16 \times 10 = 160 \] 4. Now substitute back: \[ 2 \times (160) = 2 \times 160 = 320 \] Thus, we can fill in the squares: \[ \text{c: } 32 \times 10 = 320 \] ### d Given: \[ 5 \times (3 \times 150) = (5 \times 3) \times 150 \] 1. Calculate \(3 \times 150\): \[ 3 \times 150 = 450 \] 2. Now substitute back: \[ 5 \times (450) = 5 \times 450 = 2250 \] 3. Calculate \(5 \times 3\): \[ 5 \times 3 = 15 \] 4. Now substitute back: \[ (15) \times 150 = 15 \times 150 = 2250 \] Thus, we can fill in the squares: \[ \text{d: } 15 \times 150 = 2250 \] ### Final Answers - a: \(10 + 15 = 25\) - b: \(20 + 30 = 50\) - c: \(32 \times 10 = 320\) - d: \(15 \times 150 = 2250\)