Tìm x:

a) 1998 + x = 2019	f) x + 30100 - 15100 = 60000
b) x - 3486 = 39401	g) 100000 - 30000 - x = 58000
c) x ´ 8 = 67400	h) x ´ 8 + 25 = 81
d) x : 5 = 12300	i) 72 - x : 4 = 16
e) 100000 : x = 5	k) x : 4 ´ 7 = 25200

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