B)1/10 + 1/40 + 1/88 + 1/154 + 1/138 + 1/340
B=1/2x5+1/5x8+1/8x11+1/11x14+1/14x17+1/17x20
B=1/3x(3/2x5+3/5x8+3/8x11+3/11x14+3/14x17+3/17x20)
B= 1/3x(1/2-1/20)
B= 1/3x9/20
B=3/20
C)1/2 + 1/4 + 1/8 +....+ 1/1024 + 1/2048 + 1/4096
⇒C:2=1/4+1/8+1/16++...1/2048+1/4096
⇒1/2xC=1/2+1/4+1/8+1/16+...+1/2048-1/4-1/8-1/16-...-1/4096
⇒C:2=1/2-1/4096
⇒C:2=2047/4096
⇒C=(2047x2)/4096
⇒C=4094/4096