100-20=80%=400
[tex]\\ \rm\longmapsto 80\%\:of\:CP=400[/tex]
[tex]\\ \rm\longmapsto CP=400\times \dfrac{100}{80}[/tex]
[tex]\\ \rm\longmapsto CP=5(100)[/tex]
[tex]\\ \rm\longmapsto CP=500[/tex]
Step-by-step explanation:
Given,
S.p.=Rs400
Loss percent(L%) =20%
C.p.=?
We know,
S.p. =(100-L) % of c.p.
or,400=(100-20)% *c.p.
or,400=80% *c.p.
or, 400=80/100*c.p.
or,c.p.=Rs.500
Here, c.p.=Rs.500