I can't solve 5²¹ x 4¹¹ = 2 x 10ª a=?, I know the answer is a=11, but i don't know how to get there.

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I can't solve 5²¹ x 4¹¹ = 2 x 10ª a=?, I know the answer is a=11, but i don't know how to get there.

2007-10-04 13:11:22 · 2 answers · asked by pab_flores 1 in Science & Mathematics ➔ Mathematics

I got this problem from a GMAT practice test

2007-10-04 13:20:49 · update #1

2 answers

5^21x4^11=2x10^a
5^21=5x5x5x5x5x5x5x5x5x5x5x5x5x5x5x5x5x5x5x5x5=4.77x10^14.
also 4^11=4194304
now 5^21x4^11=4.77x10^14x4194304=2x10^21
which means 2x10^21=2x10^a
divide both sides by 2 leave us with 10^21=10^a. which means a=21.
by comparing both sides of the equation.

2007-10-04 14:27:42 · answer #1 · answered by king T 1 · 0⤊ 0⤋

5Â²Â¹ x 4Â¹Â¹ = 5^10 x 5^11 x 4^11 = 5^10 * 20^11
which is way more than 2 x 10^11

Are you sure the problem is written correctly?

2007-10-04 13:17:52 · answer #2 · answered by Steve A 7 · 0⤊ 0⤋