p kg of potatoes are bought for Rs 70. Cost of 1kg of potatoes (in Rs) is __________.
Given that p kg of potatoes are bought for Rs 70.
This means
Cost of p kg of potatoes = Rs 70
Cost of 1 kg of potatoes 
25
p kg of potatoes are bought for Rs 70. Cost of 1kg of potatoes (in Rs) is __________.
Given that p kg of potatoes are bought for Rs 70.
This means
Cost of p kg of potatoes = Rs 70
Cost of 1 kg of potatoes