Adding Water Doesn't Change the SALT | GRE Dilution Trick in 60s

Added: 2026-05-26

[00:00:00]Most students get this GRE quant question wrong. Let's tackle a dilution problem that trips up a lot of students.

[00:00:06]A chemist has 100 ml of a 20% salt solution. How much pure water must be added to dilute the mixture to a 5% salt solution? First, track what stays constant. Adding pure water doesn't change the salt mass, it stays fixed.

[00:00:18]Next, find the salt mass. 20% of 100 ml means we have 20 g of salt. Now, we need a 5% solution. So, 20 g divided by 0.05 gives us 400 ml total volume. Subtract the starting volume. 400 ml - 100 ml means we need 300 ml of water to dilute it. Remember, on dilution problems, anchor to what stays constant. Here, the salt mass is key. Want more tips like this? Hit that subscribe button.