# 1. Option 1.

Find the value of the expression $101+102-103-104+105+106-107-108+\ldots-619$?
Answer: 100.

Solution. Subtract and add the number 620 at the end of the expression. Then the numbers from 101 to 620 will be divided into $(620-100): 4=130$ quartets. And in each quartet, the sum of the numbers will be equal to -4. Then the value of the expression will be equal to $(101+102-103-104)+(105+106-107-108)+\ldots-619-620)+620=$ $130(-4)+620=100$.