The temperature in the morning was - 7 ℃, which rose 11 ℃ at noon and dropped 9 ℃ in the middle of the night. What was the temperature in the middle of the night?

The temperature in the morning was - 7 ℃, which rose 11 ℃ at noon and dropped 9 ℃ in the middle of the night. What was the temperature in the middle of the night?

(- 7) + 11 + (- 9) = [(- 7) + (- 9)] + 11 = - 16 + 11 = - 5 A: the temperature in the middle of the night is - 5 ℃

The temperature in the morning was - 7 ℃, which rose 11 ℃ at noon and dropped 9 ℃ in the middle of the night. What was the temperature in the middle of the night?

(- 7) + 11 + (- 9) = [(- 7) + (- 9)] + 11 = - 16 + 11 = - 5 A: the temperature in the middle of the night is - 5 ℃

The temperature in the morning was - 7 ℃, which rose 11 ℃ at noon and dropped 9 ℃ in the middle of the night. What was the temperature in the middle of the night?

(- 7) + 11 + (- 9) = [(- 7) + (- 9)] + 11 = - 16 + 11 = - 5 A: the temperature in the middle of the night is - 5 ℃

1/(13×15)+1/(15×17)+1/(17×19)+… 1/(37×39)=

1/（13*15）=[1/13-1/15]/2
1/（15*17）=[1/15-1/17]/2
...
1/(13×15)+1/(15×17)+1/(17×19)+… 1/(37×39)=[1/13-1/39]/2
=1/39

In the trapezoid ABCD, if the diagonal lines AC and BD are equally divided, and AC = 8 and BD = 6, the height of the trapezoid is ()

Trapezoidal diagonal never bisect, draw your own picture to know that this is a diamond

1 + 2 + 3 + +1999+2000+2001+2002 ②1+3+5+… +17+19

①1+2+3+… +1999+2000+2001+2002
=（1+2002）×2002÷2
=2003×1001
= 2005003
②1+3+5+… +17+19
=20×20
=400

What is the sum of 518 of 27 and 23?

27 × 518 + 23 = 712 + 23 = 816

Five minus three times y minus one third is three

Y = 5 / 3 is 5 / 3

5 out of 9 times 5 by 18

5/9*5*18
=25*2
=50

5 out of 7 times 4 out of 9 times 7 out of 10

14/63