Question

A piece of fruit weighs 90 grams and is 80% water. It is dried out and some of the water
is removed. After this, the fruit is only 40% water. How many grams does it now weigh?

(The explanation is: "At first , the fruit consists of 72 grams of water and 18 grams of other material. After
drying out, it still has 18 grams of other material, but now this is 60% of its total mass, so
the total mass must be 30 grams.")
My question is: How did they arrive at 30?

Answer 1

Let x = total mass
x= .40x + 18
.6x=18
x=18/.6=30

Answer 2

Did you follow that?

Answer 3

Let x = total mass.
total mass is 60% water + the original non-water material (18 grams)
.40 is 40% converted to a decimal
so then we would have: x=.40 x +18 subtract .40x from both sides
getting .6x = 18
x=30

Answer 4

Good luck with these.