book Maths Puzzle Numerical Ability

Take any number. Add 10, multiply by 2, add 100, divide by 2 and subtract the original number. The answer will be the number of minutes in a hour. Why?

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Work Problems
Jenny has bought a new condo. The closing has been set for 45 days from today. The builder estimates that the remaining work on the condo will take about 750 hours t Probability problem:

There are 5 red and 4 black balls in a box. If you pick out 3 balls without replacement, what is the probability of getiing at least one red ball?

I have tried so far: P(5/9) + P(4/9) - (3/9)= (6/9)≈ 2/3