Respuesta :

51.7 rouded would be 50  and 9 is closer to 10 so 50 times 10 is 500


51.7 -> 50
9 -> 10

(keep in mind that I'm rounding to the nearest 10 ok?)

50
X 10
-----------
00
+ 500
------------
500

51.7 x 9= 500 (estimated)