Cost price of 1 pencil box = C.P = Rs 30
∴ Cost price of 10 pencil boxes = Total C.P = Rs 30 × 10 = Rs 300
Selling price of 10 pencil boxes = Total S.P = Rs 290
Since, Total C.P > Total S.P, a loss is incurred.
Loss = Total C.P ˗ Total S.P
= Rs 300 – Rs 290
= Rs 10