Given = $$(a-b):(b-c):(c-d)=1:2:3$$
=> $$\frac{a-b}{b-c}=\frac{1}{2}$$
=> $$2a-2b=b-c$$
=> $$2a+c=3b$$ -----------(i)
Similarly, $$\frac{b-c}{c-d}=\frac{2}{3}$$
=> $$3b-3c=2c-2d$$
=> $$3b=5c-2d$$ ----------(ii)
Substituting above value in equation (i), we get :
=> $$2a+c=5c-2d$$
=> $$2a+2d=5c-c$$
=> $$2(a+d)=4c$$
=> $$\frac{a+d}{c}=\frac{4}{2}=2$$
$$\therefore$$ $$(a+d):c=2:1$$
=> Ans - (B)
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