Answer:
ksh 140.
Explanation:
when a watch is sold at ksh.126 a loss of x%. This can be summarised as follow:
Selling price (Sp) = ksh 126
Percentage loss = x%
Cost price (Cp) =?
Percentage loss = Cp – Sp/Cp x 100
x% = Cp – 126/Cp .......(1)
if sold at ksh.154 a profit of x% is realized. This can be summarised as follow:
Selling price (Sp) = ksh 154
Percentage gain = x%
Cost price (Cp) =?
Percentage gain = Sp – Cp/Cp x 100
x% = 154 – Cp/Cp..... (2)
Equating equation 1 and 2, we have:
x% = Cp – 126/Cp .......(1)
x% = 154 – Cp/Cp..... (2)
Cp – 126/Cp = 154 – Cp/Cp
Cross multiply
Cp(Cp – 126) = Cp(154 – Cp)
Cancel out Cp
Cp – 126 = 154 – Cp
Collect like terms
Cp + Cp = 154 + 126
2Cp = 280
Divide both side by 2
Cp = 280/2
Cp = 140
Therefore, the cost price otherwise known as the buying price is ksh 140.