Tìm x: a) 1998 + x = 2019

a)

1998 + x = 2019

x             = 2019 – 1998

x             = 21

b)

x – 3 486 = 39 401

x          = 39 401 + 3 486

x          = 42 887

c)

x × 8 = 67 400

x = 67 400 : 8

x = 8 425

d)

x : 5 = 12 300

x = 12 300 × 5

x = 61 500

e)

100 000 : x = 5

x             = 100 000 : 5

x             = 20 000

f)

x + 30 100 – 15 100 = 60 000

x + 30 100 = 60 000 + 15 100

x + 30 100 = 75 100

x = 75 100 – 30 100

x = 45 000

g)

100 000 – 30 000 – x = 58 000

                  70 000 – x = 58 000

                                 x = 70 000 – 58 000

                                 x = 12 000

h)

x × 8 + 25 = 81

x × 8 = 56

x = 56 : 8

x = 7

i)

72 – x : 4 = 16

    x : 4 = 72 – 16

    x : 4 = 56

         x = 56 × 4

         x = 224

k)

x : 4 × 7 = 25 200

x : 4 = 25 200 : 7

x : 4 = 3 600

x = 3 600 × 4

x = 14 400