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# Manipulating quadratic and exponential expressions — Basic example

Watch Sal work through a basic Manipulating quadratic and exponential expressions problem.

## Want to join the conversation?

• why make things so much harder if all you have to do is plug in for the exponent of 2. you get the same answer of .7225
• Things were made simpler. That was 10 times smarter, and a 100 times faster.
• Why make things more complicated? This could have been answered with common sense, 85% of 85% is going to be less than .85 so you pick A because that is the only one that is less than .85 and move on.
• Sometimes when your under a time crunch, you don't detect the simple tricks you could use and instead use methods you're more familiar with even if they're more complicated and time-consuming.
• This isn't a question. But a quicker way is:
when the last digit of 2 different values add up to 10, and the first digit(s) are the same, you can simply multiply the first digit(s) by the next digit(s) in succession. Then multiply the last digits by one another and put it behind the former.
85 * 85 //5 + 5 = 10; both have the same digit in the tens place so
9 * 8 = 72
7225

24 * 26 = 624 // 6 + 4 = 10; 5 * 4 = 24
123 * 127 = 15621 // 12 * 13 = 156; 3 * 7 = 21
• Wouldn't you just put 2 in place of t and solve that way?
• If you put 2 in place of the variable that means you do this:
V(t)=24900*0.85^2
V(t)=24900*0.7225
V(t)=17990.25
I am very confused, wouldn't it be be (D), because you also multiply by 24900.
Thank you
• Okay so option D says 1.7 right?? which isn't correct in this case...You are right, we multiply by 24900 to get the value two years later, but we also have to divide it by the current value since the question says "how many times its present value" and the present value is 24900, so it is effectively (24900*(0.85^2))/24900 which is just 0.85^2=0.7225
• Or...you could just multiply 0.85 by itself because after two years it will be 85% of 85%. It could be 30 seconds rather than 3 minutes.
• I think that all you people are talking about another lesson, rather than talking about what Sal is explaining.
I would say there some issues with that video, maybe it mix up with another video.
• You don't need to solve the question the answer is obvious by elimination