72

 

 

Step-by-step explanation

∑x_i = X₁ + X₂ + X₃ + X₄ + X₅ ; i =1. . .5

Where

X₁ = 18

X₂ = 20

X₃ = 18

X₄ = 8

X₅ = 8

 

Hence, substituting the values into the formula, we obtain

 

∑x_i = 18 + 20 + 18 + 8 + 8

 

∑x_i = 72

 

 

Reference

 

Carpenter, T. P., & Moser, J. M. (2020). The development of addition and subtraction problem-solving skills. In Addition and subtraction (pp. 9-24). Routledge.