Apples lose 71% of their weight while drying. how many fresh apples to you need to pick in order to get 128 lb of dried apples?

100-71=29

71% lost means 29% remains

you want that 29% to weigh 128lb

so 29% of original=128lb

remember, percent means parts out of 100
x%=x/100 so 29%=29/100
also, 'of' means multiply

29% of original=128
29/100 times original=128
multiply both sides by 100/29
original=12800/29
original=441.37931034482758620689655172414
so about 441lb of apples must be picked