Question

If $CP$ of the $4$ pen is equal to $SP$ or $5$ pens find $p$% or $L$%
$CP$ of $4$ pens $=SP$ of $5$ pens.

Answer 1

$CP\times 4=SP\times 5$

$CP-$ Cost price

$SP-$ Selling price

$CP/SP=5/4$

Loss $=C.P-S.P$

$=1$

Loss $\%=\frac{1\times 100}{5}=20\%$