Time

Time problems on the SAT are like figuring out how long a journey takes or when something will finish. Think of it like planning a road trip: you need to know how many hours you'll drive, how many stops you'll make, and what time you'll finally arrive at your destination. It's all about measuring durations (how long something lasts) and calculating specific points in time (like an arrival time).

We mostly deal with hours and minutes. Remember there are 60 minutes in 1 hour. This is super important! It's like knowing there are 100 pennies in a dollar – you need to convert between them to get the right total. Sometimes you'll see questions about days too, and you know there are 24 hours in 1 day.

The key is to not just add or subtract numbers like they're regular numbers. When you add 30 minutes to 40 minutes, you don't get 70 minutes and then just write '70'. You get 70 minutes, which is 1 hour and 10 minutes (because 60 minutes makes an hour!). It's like when you have 10 dimes; you don't say you have '10 dimes', you say you have '1 dollar'.

Let's say you're going to a concert! The concert starts at 7:15 PM. You know it takes you 40 minutes to walk from your house to the concert hall. You also want to get there 15 minutes early to find your seat and grab a snack.

Here's how you'd figure out what time you need to leave:

1. Concert Start Time: 7:15 PM
2. Early Arrival Time: You want to be there 15 minutes before 7:15 PM. So, 7:15 PM - 15 minutes = 7:00 PM. This is your target arrival time.
3. Travel Time: It takes 40 minutes to walk. So, you need to leave 40 minutes before your target arrival time of 7:00 PM.
4. Calculate Departure Time: 7:00 PM - 40 minutes.
   • Take 40 minutes away from 7:00 PM. If you go back 30 minutes from 7:00 PM, you're at 6:30 PM. You still need to go back another 10 minutes (40 - 30 = 10).
   • So, 6:30 PM - 10 minutes = 6:20 PM.

So, you need to leave your house by 6:20 PM to make it to the concert 15 minutes early! See how we had to subtract minutes and sometimes 'borrow' from the hours?

Most time problems involve adding or subtracting durations. Here's a simple way to think about it:

1. Identify the Goal: Are you trying to find a start time, an end time, or how long something lasted (the duration)?
2. Break Down Times: If you're adding or subtracting, deal with the minutes first, then the hours. It's like separating your pennies and dollars.
3. Handle Conversions (The '60 Rule'): If your minutes go over 59 (e.g., 70 minutes), subtract 60 and add 1 to the hour. If you need to subtract more minutes than you have (e.g., trying to subtract 40 minutes from 10 minutes), 'borrow' 1 hour and add 60 minutes to your current minutes. (So, 1 hour becomes 60 minutes).
4. Keep Track of AM/PM: If a problem crosses noon (12 PM) or midnight (12 AM), remember that the AM/PM changes. Going from 11 AM to 1 PM means you've crossed noon.
5. Double-Check: Does your answer make sense? If you started at 8 AM and something lasted 3 hours, should the end time be 5 AM? No, that doesn't make sense!

Sometimes, the SAT will try to trick you by giving you time in different units, like hours and minutes, and asking for the total in just minutes. It's like having some money in dollars and some in quarters and needing the total amount in quarters.

1. To go from Hours to Minutes: Multiply the number of hours by 60. (Example: 2 hours * 60 minutes/hour = 120 minutes).
2. To go from Minutes to Hours: Divide the number of minutes by 60. You might get a decimal or a fraction, which is okay. (Example: 90 minutes / 60 minutes/hour = 1.5 hours or 1 hour and 30 minutes).
3. To go from Minutes to Seconds: Multiply the number of minutes by 60. (Example: 5 minutes * 60 seconds/minute = 300 seconds).
4. To go from Seconds to Minutes: Divide the number of seconds by 60. (Example: 180 seconds / 60 seconds/minute = 3 minutes).

Always look at what unit the question is asking for in the final answer!

Here are some common traps students fall into when dealing with time:

• ❌ Treating minutes like regular base-10 numbers: Adding 30 minutes and 45 minutes and getting '75 minutes' then thinking it's 1 hour and 15 minutes without actually doing the conversion. ✅ How to avoid: Always remember the '60 rule'. 30 + 45 = 75. Since 75 is more than 60, subtract 60 (75 - 60 = 15 minutes) and add 1 to the hour. So, it's 1 hour and 15 minutes.

• ❌ Forgetting AM/PM changes: Calculating an event that starts at 10 PM and lasts 3 hours, and saying it ends at 1 AM without thinking about the day change. ✅ How to avoid: Visualize a clock or a timeline. 10 PM + 1 hour = 11 PM. 11 PM + 1 hour = 12 AM (midnight). 12 AM + 1 hour = 1 AM. The day has changed!

• ❌ Miscalculating 'borrowing' an hour: Trying to subtract 40 minutes from 7:10 and incorrectly saying it's 6:70 or 6:30. ✅ How to avoid: When you 'borrow' 1 hour, it becomes 60 minutes. So, 7:10 becomes 6 hours and (10 + 60) minutes = 6:70. Then subtract: 6:70 - 40 minutes = 6:30. This is the correct way to think about it.

• ❌ Not reading the question carefully for units: The question asks for the answer in minutes, but you calculate it in hours. ✅ How to avoid: Underline or circle the units requested in the final answer. Convert at the very end if needed, or convert all numbers to the required unit at the beginning.