emmak wrote:

The product of the first 10 prime numbers is closest to which of the following?

A. 6.5 x 10^7

B. 6.5 x 10^8

C. 6.5 x 10^9

D. 6.5 x 10^10

E. 6.5 x 10^11

1st 10 Prime Number- 2,3,5,7,11,13,17,19,23,29

Let Product of 1st 10 Prime Number\(=P\)

Therefore \(P=2*3*5*7*11*13*17*19*23*29\)

Now approximating following as

\(5*13=65\)

\(2*3*7\approx{40}\)

\(11\approx{10}\)

\(13\approx{10}\)

\(17\approx{20}\)

\(19\approx{20}\)

\(23\approx{20}\)

\(29\approx{30}\)

Therefore \(P=65*40*10*10*20*20*20*30\)

\(P=65*8*10^7\)

\(P=65*10*10^7\) (as \(8\approx{10}\))

\(P=65*10^8\)

\(P=6.5*10*10^8\)

\(P=6.5*10^9\)

Therefore Option 'C'

Thanks

Dinesh