Antifreeze
How much more antifreeze is needed to make the proportion 30%?
Age
14 to 16
Challenge level
Problem
A large container holds 14 litres of a solution that is 25% antifreeze, the remainder being water. How many litres of antifreeze must be added to the container to make a solution that is 30% antifreeze?
If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.
Student Solutions
Answer: 1
Using proportion
Image
4.5 litres of antifreeze in new mixture
1 more litre needed
Using algebra
Let the extra volume of antifreeze required be $x$ litres. Initially, there are 3.5 litres of antifreeze in the solution. So $3.5+x=0.3(14+x)$, that is, $35+10x=42+3x$, so $x=1$.