+103 in a pool there is a certain amount of water ( not known) . added to the pool 160 L of water, after that reduced the water amount by 10%, and finaly took out of the pool 195 L of water. at the end of the process the pool remained with 225 L of water.
1) what was the amount of water in the pool before the process?
2) did at the end of the process the water amount in the pool reduced or rised in %? if so then in how much precent %?
pls help 
+33615 Start by letting the original volume of water in the pool be, say, w litres.
First step is to add 160 to this: w+160
Reducing the result by 10% is to be left with 90%: (w+160)*0.9 (0.9 is 90% as a fraction).
Take out 195 litres: (w+160)*0.9 - 195, and this equals 225, so:
(w+160)*0.9 - 195 = 225
Add 195 to both sides: (w+160)*0.9 = 420
Multiply both sides by 10/9: w+160 = 4200/9 = 466.67 (actually 466 and two-thirds)
Subtract 160 from both sides to get: w = 306.67
+33615 Start by letting the original volume of water in the pool be, say, w litres.
First step is to add 160 to this: w+160
Reducing the result by 10% is to be left with 90%: (w+160)*0.9 (0.9 is 90% as a fraction).
Take out 195 litres: (w+160)*0.9 - 195, and this equals 225, so:
(w+160)*0.9 - 195 = 225
Add 195 to both sides: (w+160)*0.9 = 420
Multiply both sides by 10/9: w+160 = 4200/9 = 466.67 (actually 466 and two-thirds)
Subtract 160 from both sides to get: w = 306.67
+118608 i admit i haven't the time to look properly but I doubt that there is anything wrong with Alan's answer so I am ticking it.
+103 i understand everything in your answer alan but all untill the part that you say to multiplay it all by 10/9, why 10/9 if its 0.9? is it because i switch the sides of the 0.9?
+33615 "i understand everything in your answer alan but all untill the part that you say to multiplay it all by 10/9, why 10/9 if its 0.9? is it because i switch the sides of the 0.9?"
Sorry, I should have explained more carefully! 0.9 is the same as 9/10, so by multiplying by 10/9 we eliminate it from the left-hand side of the equation. Perhaps I should have simply said divide both sides by 0.9.
+103 
+33615 For the second part:
At the end there is 225 L (the value given)
At the start there is 306.67 L (the value of w that we've just worked out)
So we end up with less than we started with.
Express end as a percentage of start by dividing 225 by 306.67 and multiplying by 100:
$$\left({\frac{{\mathtt{225}}}{{\mathtt{306}}}}\right){\mathtt{\,\times\,}}{\mathtt{100}} = {\mathtt{73.529\: \!411\: \!764\: \!705\: \!882\: \!4}}$$
At the end we have about 73.5% of what we started with. Therefore we have a reduction of (100-73.5)% or 26.5%
