Question

tìm x

a, x + 1/2x - 25%x = 10

b, x+x - 1+ x - 2 + x -3 + x - 4 + ... + x-50 = 255

c, 1 + 5 + 9 + 13 + 16 + ... + x =501501

Answer 1

b, x+x-1+x-2+...+x-50=255

=>x+x+x+...+x-1-2-3-4-...-50=255

=>x.51-(1+2+3+...+50)=255

=>x.51-[(50+1).(50-1+1):2]=255

=>x.51-[51.50:2]=255

=>x.51-1275=255

=>x.51=255+1275=1530

=>x=1530:51=30

Vậy x = 30

Answer 2

a, x + 1/2x - 25%x = 10

=> x + 1/2x - 1/4x = 10 => x.( 1/2 - 1/4 ) =10 => x.1/4 = 10 =>x = 10 : 1/4 = 40 Vậy x = 40