Question

the cost of 5 pencils is equal to the selling price of 4 pencils. fond the gain percent

Answer 1

difficult one. is price not given. if it is then subtract cp from so and then divide the result with cp and then multiply it with 100%

Answer 2

Given, C.P of 5 pencils = S.P of 4 pencils

5 C.P = 4 S.P
C.P/S.P = 4/5
C.P:S.P = 4:5
C.P = 4........S.P = 5
Gain% = Gain/C.P * 100 = 1/4 * 100 = 25%

OR
Assume C.P of 1 pencil = '' Rs.
C.P of 5 pencils = 5X rs.
S.P of 4 pencils = C.P of 5 = 5X Rs.
C.P of 4 pencils = 4X Rs.
Hence Gain = 5X - 4X = X rs.
Gain% = X/4X * 100 = 25%
[Alternatively, you can also solve by assuming any numeric value for C.P]
Hope it helps