help with this problem thks

nubianj

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inthe sequence of numbers x1, x2,x3,x4,x5 each number after teh first is twice the preceding number. if x5-x1 is 20 what is the value of x1
the answer choices are 4/3, 5/4, 2, 5/2, and 4. thanks for ur help
 
nubianj said:
inthe sequence of numbers x1, x2,x3,x4,x5 each number after teh first is twice the preceding number. if x5-x1 is 20 what is the value of x1
the answer choices are 4/3, 5/4, 2, 5/2, and 4. thanks for ur help

x<sub>1</sub> is the first term. And each term after that is 2 times the preceding term. So,

x<sub>2</sub> = 2 * x<sub>1</sub>
x<sub>3</sub> = 2 * 2 * x<sub>1</sub>, or 4 x<sub>1</sub>
x<sub>4</sub> = 2 * 2 * 2 * x<sub>1</sub>, or 8 x<sub>1</sub>
x<sub>5</sub> = 2 * 2 * 2 * 2 * x<sub>1</sub>, or 16 x<sub>1</sub>

Ok....you know this:
x<sub>5</sub> - x<sub>1</sub> = 20

Substitute 16 x<sub>1</sub> for x<sub>5</sub>:

16 x<sub>1</sub> - x<sub>1</sub> = 20

And solve for x<sub>1</sub>..........

I hope this helps you.
 
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