Question

20 + 80 + x = 400

Answer 1

20 + 80 + x = 400

80 + x = 400 - 20

80 + x = 380

x = 380 - 80

x = 300

Answer 2

x=300

Answer 3

Theo đề ta có:

20 + 80 + x = 400

100 + x = 400

x = 400 - 100

x = 300