21. Approximately how long is a millionth, defined to be one-thousand of a month (a) 20 secs (b) 70 secs (c) 8 mins (d) 40 mins (e) 3 hours

24. In this expression
☐ 1/3 ☐ 1/4 ☐ 1/5 ☐ 1/6 ☐ 1/7
We place either a plus sign or a minus sign in each box so that the result is the smallest positive number possible

(a) between 0 and 1/100 (b) between 1/100 and 1/50
(c) between 1/50 and 1/20
(d) between 1/20 and 1/10
(e) between 1/10 and 1