Choose the correct answer for each number then include a brief solution /explanation for each

17. Danny and Roy can do a piece of work in 42days Roy and Vicoy in 31 days and Vicoy and Danny in 20 days , In approximately how many days can all of them do the work together? A. W B. 19 C. 17 D. 10 18. In a three digit number, the hundreds digit is twice the units digit. If 3% be subtracted from the number, the order of the digits will be reversed. Find the number if the sum of the digits is 17. A. 458 B. 683 C. 386 D. 854 19. A watch which gains 5sec. in 3 min. was set right at 7 am In the afternoon of the same day, what is the true time when the watch indicated quarter past 4 . 'clock? A. 59 /12 min past 3 pm C. 2 min. past 4pm B. D. 4 10m 58 . min past 3 pm