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# Adding & subtracting rational numbers: 79% - 79.1 - 58 1/10

Sal evaluates 79% - 79.1 - 58 1/10. Created by Sal Khan.

## Want to join the conversation?

• 𝐻𝑜𝓌 𝒹𝑜 𝓎𝑜𝓊 𝒻𝒶𝒸𝓉𝑜𝓇 𝑜𝓊𝓉 𝒶 𝓃𝑒𝑔𝒶𝓉𝒾𝓋𝑒 𝓈𝒾𝑔𝓃?
• Essentially, to factor a negative number, find all of its positive factors, then duplicate them and write a negative sign in front of the duplicates. For instance, the positive factors of −3 are 1 and 3.
• i thought when you change a subtraction sign to a plus sign then the number behind it would become negitive? Please explain this to me because this video just confused me?
• minusing a negative is the same thing as adding a positive
• At he talks about "factoring out" a negative sign what exactly is this and what is it used for?
• This is so confusing! Can someone explain it with this question? I'm having a bit of trouble with this one;

-45/40 + 1.875=
• First convert either of the numbers to the same format as the other one. E.g., decimal, fraction.
-45/40 = -1 5/40 = -1 1/8 = -1.125
Now solve the equation:
-1.125 + 1.875 = 1.875 - 1.125 = 0.75
(1 vote)
• At , Sal factors out a negative sign. Can someone explain to me what that it is and why he did it? Also, can you explain how they became positive? Thanks!
• 𝚠𝚑𝚎𝚗 𝚢𝚘𝚞 𝚏𝚊𝚌𝚝𝚘𝚛 𝚘𝚞𝚝 𝚊 𝚜𝚒𝚐𝚗, 𝚏𝚕𝚒𝚙 𝚝𝚑𝚎 𝚜𝚒𝚐𝚗𝚜. 𝚎𝚟𝚊𝚕𝚞𝚊𝚝𝚎 𝚋𝚘𝚝𝚑 𝚜𝚒𝚍𝚎𝚜 𝚖𝚊𝚔𝚒𝚗𝚐 𝚜𝚞𝚛𝚎 𝚝𝚑𝚎 𝚎𝚚𝚞𝚊𝚝𝚒𝚘𝚗 𝚒𝚜 𝚌𝚘𝚛𝚛𝚎𝚌𝚝. 𝚜𝚘𝚛𝚛𝚢 𝚒𝚏 𝚝𝚑𝚊𝚝 𝚍𝚒𝚍𝚗'𝚝 𝚑𝚎𝚕𝚙.
• Did Sal make Khan academy?
• im confused why did he turn 79% into .79?
• Percent means you divide by 100, so then 79% would be 79/100 which is 0.79. Hope this helps.
• How do you calculate an addition/subtraction equation that starts with a negitive decimal and the rest are postive decimals?
• To give an example, are you talking about a question like this?
-.325 + .585?
If that is the case, then think of it like this. If the question is adding, and the negative decimal comes first, then do this. .585 -325. That should give you the answer.
If you are multiplying, such as this,
-.325 x .585
it's the same thing as multiplying negative numbers. Multiplying a negative number by a positive number will get you a negative number. So, do this. Take the decimals out, and multiply. You should get this equation.
-325 x 585= -190125.
Now, since you took 6 decimal places out, put 6 in. Your final answer should be -.190125.
If you are subtracting like this,
-.325 - .585,
that 585 will actually ADD to the negative -.325, making it -.910.
If you are dividing, think of it as the same thing as multiplying. Good luck!