Question

you are having 100 rupees and you should buy 100fruits
one apple = 1 rupee
one mango = 1 rupee
twenty bananas = 1 rupee
while you are buying you should buy the three fruits
for example
some apples + some mangoes + some bananas = 100 fruits
and you must spent 100 rupees
DON'T ANSWER SILLY

Answer 1

This is not possible because

Let there are
x apples
y mangoes
z banana

their price are
apple = 1rs
mango = 1rs
banana = 1/20 rs

total prices are
apple = x rs
mangoes = y rs
banana = z/20 rs

total fruits = 100
i.e. x + y + z =100 .....(1)

total money = 100
i.e. x + y + z/20 =100 ......(2)

comparing eqn 1 and 2
z = z/20
i.e. z = 0

which can't be possible according to question one have to buy all three fruits

Hope this is helpful

Answer 2

z=0, some value for z is not possible.