Question

How many 5 - digit numbers have the second digit odd and the fifth digit at least four times the second digit?

Answer 1

53

Why :

this is type of casework

- B can only be 1

so E = 4

9 x 1 x 10 x 10 x 1 = 900

and so, theres only one possible.

Answer 2

Answer: 908 5-digit numbers

Step-by-step explanation:

example of 5 digit number with conditions met: 11004

Total number of 5 digit numbers:

99999-10000+1=

100000-10000=90000 5 digit numbers

2nd digit: 5th digit possibilities

y>=4x

x: y

1: 4, 5, 6, 7, 8, 9 ==> 6 digit options

2: 8, 9 ==> 2 digit options

How about remaining digits?

5-2=3 remaining digits to fill

Random Selection for other 3 digits(1-9):

1: 00-99 ==> 99-0+1=99+1=100 digit options

2: 00-99 ==> 99-0+1=99+1=100 digit options

.

.

9: 0-99 ==> 99-0+1=99+1=100 digit options

9*100=900

900+6+2=908 5-digit numbers