$a)1407\approx 1400$   

$78896\approx 78900$   

$23907\approx 23900$  

$107961\approx 108000$  

$347999\approx 348000$  

 

$b)1407\approx 1000$  

$78896\approx 79000$  

$23907\approx 24000$  

$107961\approx 108000$  

$347999\approx 348000$