Answer: No, she did not study for at least 15 hours.
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Step-by-step 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
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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".