1, starting from 2 in the lower left corner, fill in "+"or "-"between the numbers so that the final result is equal to 7.

2 4 6 9 5 1 = 7

2. The small conference room of the school has four seats in the first row, with two more seats in each row than in the previous row, and the last row has 18 seats. How many seats are there in this conference room?

Answer analysis:

1, starting from 2 in the lower left corner, fill in "+"or "-"between the numbers so that the final result is equal to 7.

2 4 6 9 5 1=7

2 + 4 + 6 – 9 + 5 – 1 = 7

2. The small conference room of the school has four seats in the first row, with two more seats in each row than in the previous row, and the last row has 18 seats. How many seats are there in this conference room?

(18-4) ÷ 2+ 1 = 8 (row)

(18+4)×8÷2=88 (pieces)