Question

if the cp of 10 notebook is equal

Answer 1

cp of 1 note book is 100/10=10
so of 1 note book is 100/8=12.5
cp-sp=2.5

Answer 2

let the CP of 10 notebooks and SP of 8 notebooks be = 100

C.P of 1 notebook = 100/10 = 10Rs
S.P of 1 notebook = 100/8 = 12.5Rs
Profit = S.P - C.P
             12.5 - 10
             2.5Rs
loss% = loss/C.P * 100
            2.5/10 * 100
            25%