Solution: Suppose this number X.

x+x+x-x+x*x+x/x= 100

Assuming that an empty cup weighs x and a glass of water weighs y, the following results are obtained:

x+3y=440，x+5y=600

So: x=200, y=80.

Suppose grandpa is x years old and the topic is:

X+x/2+ 1= 100, so x=66, which means grandpa is 66 years old this year.