Tammy figured her math exam would be difficult unless she put in at least 15 hours of study time to prepare. She studied 2½ hours on
Monday, 3 hours on Tuesday, 4¾ hours on Wednesday, and 4 ½
hours on Thursday. Did she study for at least 15 hours? Explain.

No, she did not study for at least 15 hours.

Explanation:

Fractions are often a pain, so I find it easier to convert to decimal form whenever possible.

1/2 = 0.5

3/4 = 0.75

which lead to,

2 & 1/2 = 2 + 1/2 = 2 + 0.5 = 2.5

4 & 3/4 = 4 + 3/4 = 4 + 0.75 = 4.75

4 & 1/2 = 4 + 1/2 = 4 + 0.5 = 4.5

We can then rephrase the problem like so:

"She studied 2.5 hours on Monday, 3 hours on Tuesday, 4.75 hours on Wednesday, and 4.5 hours on Thursday"

Add up those decimal values to get:

2.5 + 3 + 4.75 + 4.5 = 14.75

In total, Tammy studied for 14.75 hours, which is equivalent to 14 & 3/4 hours.

This result is smaller than 15, so she did not study for at least 15 hours.

Note: "at least 15" is the same as saying "15 or more".