Question 1169761
<br>
You have received, to this point, three algebraic solutions to the problem, showing a variety of different levels of complexity -- emphasizing, as noted in the solution from tutor @ikleyn, that the way you set up the problem can make a big difference in the amount of work required to solve it.<br>
It is probable that a formal algebraic solution was wanted for this problem.  But note that an informal solution using logical reasoning will give you some good brain exercise; and it will get you to the answer with relatively little effort.<br>
When the number of children is reduced by 5, the amount of money each one gets is doubled, from $20 to $40.<br>
That means when the number of children is reduced by 5, the number of children is cut in half.<br>
That means the original number of children was 10 and the reduced number of children was 5.<br>
And that means the amount of money was 10 times $20, which is $200; or, alternatively, it was 5 times $40, which of course is also $200.<br>