Question

(i) How many numbers are there between 99 and 1000 having 7 in the units place?
(ii)
How many numbers are there between 99 and 1000
having
atleast one of their
digits 7?

Answer 1

@TessaMarie08181997 @mikaela19900630

Answer 2

@qweqwe123123123123111 HELP ME

Answer 3

@Noemi95 @hannahh<3

Answer 4

I got 90 for (i)

Answer 5

Yup, basically ab7, a is not zero, that leaves 9 choices for a and 10 for b. Give me a minute on 2.

Answer 6

(ii) With that same abc format, a must still not be zero, a has nine options, b and c have ten. If a is the seven, we have 100 options (700-799). If b or c is the seven, there are 90 options each for the other numbers. That's 280. However, we've just double-counted several numbers. If a and b or a and c are sevens, there are 10 possibilities (meaning there are ten numbers like each of these: 770-779 and 707, 717.... 797) so that's 20. 260 left, so what if b and c are seven? There go 9 more, leaving 251. 777 was removed three times, so we have to put it back in for 252 in total.

Answer 7

Thank you Sir