A number is formed by writing the first 10 primes in the increasing order.Half of the digits are now crossed?

Question

out so that the number formed by the remaninig digits with out changing the order is as large as possible the second digit from the left of the new number is
a)2
b)3
c)5
d)7

Answer 1

The numbers we would use are 2, 3, 5, 7, 11, 13, 17, 19, 23, and 29. There are 16 digits total, so we would cross off 8 of the digits to make a number as large as possible. To do this, cross off 2, 3, 5, 1, 1, 1, 3, and 1. So the number is now 77192329. Thus, the second digit from the left is 7. Hope this helps. :-)

Answer 2

D - 7

2 3 5 7 11 13 17 19 23 29
7 7 19 23 29

77,192,329
will be the largest number possible

Answer 3

the 10 primes written down is:

2357111317192329 ... having 16 digits (4 1-digit and 6 2-digits)
we need to cancel out 8 digits

scanning from the leftmost, we see that 7 is a high number, we need to keep it...so we cancel 235 to get "7111317192329"

we need to cancel 5 more digits....scanning from 7 we note that another 7 appears after canceling 5 digits...just as we want...

so we are left with "77192329"... this is the biggest number as desired....

so the second digit is obviously '7'

note: a recent junior olympiad question

Answer 4

B) 3

Answer 5

2357111317192329

x3x7x1x3x7x9x3x9

37137939

d) 7