Question 1163137
A box contained 50Cents coins and 20 cents coins in the ratio 2:3.when I took out foor 50Cents coins, exchanged them for 20 cents coins. And then put the money back in the box, the ratio became 2:7. Find the sum of money in the box.
<pre>I agree with Tutor @IKLEYN. 
Although not stated, the four (4, NOT foor) 50c coins that were removed were NOT replaced with 4 20c coins.
The four 50c coins, with a value of $2 were replaced with 20c coins worth $2, and that's 10 20c coins.
By letting the multiplicative factor be x, we get: {{{matrix(1,3, (2x  -  4)/(3x + 10), "=", 2/7)}}}, and subsequently, x = 6.
So, with the multiplicative factor being 6 - leading to 12 original 50c coins worth $6, and 18 original 20c coins worth $3.60 - the sum in box = {{{highlight_green(matrix(1,3, 6 + 3.60, "=", "$9.60"))}}}