Four different stores have the same digital camera on sale. the original price and discounts offered by each store are listed below. rank the stores from the cheapest to most expensive sale price of the camera.
store a: price $99.99 and discount of 15%
store b: price $95.99 and discount of 12%
store c: price $90.99 and discount of 10%
store d: price $89.99 and successive discounts of 5% and 5%

I think we have to calculate the actual prize - the estimations would be too hard.
So:

A: 99.99*(100%-15%)=99.99*85%=84,99

B: 95.99*(100%-12%)=99.99*88%=84,47

C: 90.99*(100%-10%)=90.99*90%=81.89 (this one looks the best so far)

D: 89.99*(100%-5%)=89.99*85%= 85.07(first discount)

85.07.99*(100%-5%)=.85*07%=80.81 (second discount - this is cheaper than option C).

So, from the cheapest to most expensive: D, C, B, A