$7.50. If you guessed $10, don’t feel bad. Percentages can be counter intuitive.

First job: $10/hour
Second job: $10/hour – ($10 &times .5) = $5/hour
Third job: $5/hour + ($5 × .5) = $7.50

I2.

Each entry is a letter, in alphabetical order starting with A, followed by the number of occurrences of that letter in the phrase “What is the secret to this”.

There’s one ‘a’, thus we get A1. There are no ‘b’s so it doesn’t appear, then there’s one ‘c’, and so on.

They all fall in the middle.
15 February was the middle of February (1984 being a leap year).
2 July was the middle day of the year 1983.
And 16 December was the middle of December.

Arrange the nine matchbox sticks like so to make the shape of the number ten:

        _
    /| | |
     | |_|

Since the bridge is 4 kilometers long, the halfway point would be 2 kilometers. The 18-wheeler would have used much more than 30g of fuel to drive 2 kilometers.

2178

4 × 2178 = 8712