We have a question: Donald went to a computer store. He saw a 15% reduction in the price of the laptop he wants to buy. If the laptop originally costs $800, how much will he pay for the laptop?
And an answer: 680
So how you got the answer?
There was $800 x 15 / 100 = $120. Thus, Donald will pay $800 - $120 = $680.

We have a question: Jan enters a double dutch competition. After training she doubles her speed which used to be 70 skips per minute. How many skips does she do in 5 minutes?
And an answer: 700
So how you got the answer?
She does 70 * 2 = 140 skips a minute. So he does 140 * 5 = 700 skips in the 5 minutes.

We have a question: A housewife goes to the market. She spent 2/3 of her $150. How much does she have left?
And an answer: 50
So how you got the answer?
The housewife has 3 / 3 - 2 / 3 = 1 / 3 of $150 left. This means she has $150 * (1 / 3) = $50 left.