正の数のたし算とひき算

 $\left(-14\right)+\left(+16\right)$  

(a)  

 $\left(-23\right)+\left(-15\right)$  

(a)  

 $\left(+15\right)+\left(-31\right)$  

(a)  

 $\left(-25\right)+\left(+43\right)$  

(a)  

 $\left(-11\right)+\left(+9\right)+\left(+21\right)$  

(a)  

 $\left(-15\right)+\left(-8\right)+\left(+12\right)+\left(+8\right)$  

(a)  

 $\left(+12\right)-\left(+8\right)$  

(a)  

 $\left(+16\right)-\left(+23\right)$  

(a)  

 $\left(-15\right)-\left(+17\right)$  

(a)  

 $\left(-31\right)-\left(-17\right)$  

(a)