Answer:
8421
Step-by-step explanation:
8050 < abcd < 8500
We must have a = 8, so the number is 8bcd.
The value of a is 20 times the value of b, or a= 2b.
a = 8, so b = 4.
The value of b is 20 times the value of c, or b = 2c.
b = 4, so c = 2.
The value of c is 20 times the value of d, or c = 2d.
c = 2, so d = 1.
The secret number is 8421.
