Răspuns:
a ) x + 25 + 75 = 400
x + 100 = 400
x = 400 - 100
x = 300
b) 1+2+3+....+10+ x =3000
55 + x = 3000
x = 3000 - 55
x = 2945
c) 51 +( x +23)+26=100
(x+23)+26=100-51
(x+23)+26=49
x+23=49-26
x+23=23
x=23-23
x=0
d) 1+2+3+4+x +6+7+8+9=550
10+x+30=550
x+30=550-10
x+30=540
x=540-30
x=510
e) 49+x+21+230=2312
x+21+230=2312-49
x+21+230=2263
x + 251= 2263
x = 2263-251
x = 2013
f) 22+33+44+x +188+177+166=1000
99+x +531=1000
99+x=1000-531
99+x=469
x=469-99
x = 370
