Which came first? Reading a timeline

Example 1

1. Read the tick marks first. The labels go 1770, 1780, 1790, 1800, 1810, so each tick is 10 years. Earlier is to the left.
2. A bar shows something that lasted for years: it starts at its left end and stops at its right end. A dot shows one year.
3. Two things were going on at the same time when their marks share some years: one begins before the other ends. Look straight down from the ends of each bar to the scale.
4. The American Revolutionary War bar ends in 1783. The French Revolution bar does not begin until 1789. There is a gap between them, so A is out. The war also ended long before the Haitian Revolution (1791) and the Louisiana Purchase (1803), so C and D are out too.
5. The French Revolution bar runs from 1789 to 1799. The Haitian Revolution bar begins in 1791, before the French bar ends. From 1791 to 1799 the two bars stand over the same years. That is B.
6. A good habit: for each pair, ask “Did one end before the other began?” If yes, they did not overlap.

Answer: B

Example 2

1. The library’s dot has no year printed beside it, so the only way to find its year is the scale. Read the tick marks before the events.
2. Look at the labels: 1880, 1900, 1920, 1940, 1960. They go up by 20 years.
3. Now count the spaces between two labels. From 1920 to 1940 there are two spaces, with an unlabeled tick in the middle. So each space is 20 ÷ 2 = 10 years, and the unlabeled tick between 1920 and 1940 stands for 1930.
4. Follow the dashed line down from the library’s dot. It lands on that unlabeled tick, one tick past the 1920 label: 1920 + 10 = 1930. That is B.
5. A and C are the labels on either side of the dot. They are the nearest printed numbers, which is why they tempt, but the dot is on neither of them.
6. D, 1925, comes from guessing that each tick is 5 years. Always work out the tick size from two labels first.

Answer: B