Pg 345 Question 23, 6th Edition KH Rosen [closed]

Question

How many strings of three decimal digits

1. do not contain the same digit three times?
2. have exactly two digits that are 4s?

I know question is easy but the answer is not matching with the one given over here

Please someone verify..

Does the word “string” mean that we can take 0 as the first digit as well?

Comments

a)  do not contain the same digit three times = number of strings possible - contain the same digit three times

                                                                                         = 10 x 10 x 10 - 10 x 1 x 1

                                                                                         = 1000 - 10

                                                                                         =  990

b) have exactly two digits that are 4s =  1 x 1 x 9 x 3 =  27

I didn't open the link..

but is it correct ???

---

Yes it is correct..

I didn't register the word "strings" and was calculating it by considering 3 digits decimal number :P

---

@MiNiPanda hoye hoye :p

---

@Magma 😂😂