goodyear2013 wrote:
If x, y, and z are integers greater than 1, and (3^27)(35^10)(z) = (5^8)(7^10)(9^14)(x^y), then what is the value of x?
(1) z is prime
(2) x is prime
OE:
(3^27)(35^10)(z) = (5^8)(7^10)(9^14)(x^y) Break up the 35^10 and simplify the 9^14
(3^27)(5^10)(7^10)(z) = (5^8)(7^10)(3^28)(x^y) Divide both sides by common terms 5^8, 7^10, 3^27
(5^2)(z) = (3)(x^y)
(1) SUFFICIENT: z must have a factor of 3 to balance the 3 on the right side of the equation.
(1) says that z is prime, so z cannot have another factor besides the 3. Therefore z = 3.
Since z = 3, the left side of the equation is 75, so x^y = 25.
The only integers greater than 1 that satisfy this equation are x = 5 and y = 2, so (1) is sufficient.
Put differently, the expression x^y must provide the two fives that we have on the left side of the equation.
The only way to get two fives if x and y are integers greater than 1 is if x = 5 and y = 2.
(2) SUFFICIENT: x must have a factor of 5 to balance out the 5^2 on the left side.
Since (2) says that x is prime, x cannot have any other factors, so x = 5.
Hi, can anyone explain how this works, please.
Split everything into prime factors:
\((3^{27})(35^{10})(z) = (5^8)(7^{10})(9^{14})(x^y)\)
\((3^{27})(5^{10})(7^{10})*(z) = (3^{28})(5^8)(7^{10})(x^y)\)
Now powers of prime factors on both sides of the equation should match since all variables are integers. If you have only \(3^{27}\) on left hand side, it cannot be equal to the right hand side which has \(3^{28}\). Prime factors cannot be created by multiplying other numbers together and hence you must have the same prime factors with the same powers on both sides of the equation.
Stmnt 1: z is prime
Note that you have \(3^{28}\) on Right hand side but only \(3^{27}\) on left hand side. This means z must have at least one 3. Since z is prime, z MUST be 3 only. You get
\((3^{28})(5^{10})(7^{10}) = (3^{28})(5^8)(7^{10})(x^y)\)
Now \(5^2\) is missing on the right hand side since we have \(5^{10}\) on left hand side but only \(5^8\) on right hand side. So \(x^y\) must be \(5^2\). x MUST be 5.
Sufficient.
Stmnt2: x is prime
If x is prime, it must be 5 since \(5^2\) is missing on the right hand side. This would give us \(x^y = 5^2\). Sufficient.
Answer (D)