In fact, it is a problem of six-dimensional linear equations: let apple =a, pineapple =b, orange =c, plum =d, grape =e, banana = f.

There are:

a+b+c+2d=20

2a+2e+c= 1 1

2a+b+d+f=2 1

c+e+3f= 15

Observing the second equation, we know that c can only be one of 1, 3, 5; The following is easy to solve.

Solve this equation by assignment method: let c= 1, then there is:

Tangzi = (1) Grape = (2)

Apple = (3) banana = (4)

Plum = (5) pineapple = (6)

The landlord can put them into the checking calculation one by one.