Answer:
The percentage of decrease is: "
33 ⅓ %" .
_____________________________________________Step-by-step explanation:____________________________________________Given:____________________________________________
10 years ago, # of illiterate people = 150 lakhs;
"Now" ; # of illiterate people = 100 lakhs ;
____________________________________________So; the decrease in the # of illiterate people = "(150 - 100) = 50 lakhs ;
____________________________________________To calculate the "percentage of decrease" :
____________________________________________ The "percentage of decrease" =
{"decrease in the # of illiterate people"} / {"# of illiterate people started with"] ;
× 100 (percent).
__________________________________________________ =

* 100 % ;
{Note that:

=

;
→ The "zeros" cancel out ;
→

* 100 % ;
=

* 100 ;
Note:

=

;
=

;
__________________________________________________→ 
* 100 =

*

;
_________________________________________________________ = 
% ;
= 
% ;
= "(100 ÷ 3) % ;
= "
33 ⅓ % " .
_____________________________________________________
Answer: The percentage of decrease is: " 33 ⅓ %" .
_____________________________________________________