a) To find the selling price (S.P.) when the cost price (C.P.) is Rs 640 and the loss percentage is 20%, we can use the formula:
S.P. = C.P. - (Loss Percentage * C.P.)
Given that the loss percentage is 20% (0.20 as a decimal), we can substitute the values:
S.P. = 640 - (0.20 * 640)
S.P. = 640 - 128
S.P. = Rs 512
Therefore, the selling price is Rs 512.
b) To find the selling price (S.P.) when the cost price (C.P.) is Rs 750 and the gain percentage is 8%, we can use the formula:
S.P. = C.P. + (Gain Percentage * C.P.)
Given that the gain percentage is 8% (0.08 as a decimal), we can substitute the values:
S.P. = 750 + (0.08 * 750)
S.P. = 750 + 60
S.P. = Rs 810
Therefore, the selling price is Rs 810.