Question 1043493
The question and description gives no indication of the count of the money; but just count of the coins.  The problem is using uppercase X for how many two-rand coins and lower case x for how many five-rand coins, but a better designed problem should or at least COULD direct to use different letters as variables to avoid possible confusion between these two.


{{{X+x=20}}}
{{{highlight(x=20-X)}}}
and
{{{highlight(X=20-x)}}}



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I read the problem description again. It is written wrongly.  Either x is how many of the two-rand coins, or x is how many of the five-rand coins.   The second sentence says, X is how many of the two-rand coins.  The third sentence being the question, asks for an expression "in terms of x" for how many five-rand coins.  Now we must question, what is x to stand for?  x is not 20; x is not X.  We have NO MEANING FOR x.


Do not capitalize a variable when it starts as the first "word" of a sentence written in English.  Being the first word of a sentence IS NOT A JUSTIFICATION to capitalize it.  


You most likely have this as your exercise:
I have 20 coins, and x of them are two-rand; and the rest are five-rand coins.  What is an expression in terms of x for the number of five-rand coins?


Let y be how many of the five-rand coins.
{{{x+y=20}}}
{{{y=highlight(20-x)}}}