*METHOD
1: Use the percents remaining*

When
30% of the water is removed, 70% remains. Then
when 40% of that 70% is removed, 60% of the 70%
remains. Thus, 0.6 × 70% = **42%
**of the original amount that remains
in the jar.

**METHOD
2: Use a convenient example **

The
answer will be the same no matter how much water
the jar starts with, so assume the jar starts
with 1000 mL of water. When 30% is removed (that
is 300 mL) then 700 mL is left. Next, 40% of 700
mL = 280 mL is removed, leaving 420 mL in the
jar. Thus 420 mL ÷ 1000 mL = 42% of the
original amount remains in the jar.