Question

13. Adrian, Robert, Tony and William have a rock band. In an experimental
studio session, each of them start singing a different musical theme repeatedly
until they end playing their themes all together. As the themes
long for 16 s, 21 s, 24 s and 28 s, the record session will long for

(a) 1’39”
(b) 3’39”
(c) 5’36”
(d) 7’00”
(e) 11’12”

Answer 1

Use LCM (Least Common Multiple) because the total time is divisible for each theme song.

16, 21, 24, 28 | 2
8, 21, 12, 14   | 2
4, 21, 6, 7        | 2
2, 21, 3, 7        | 2
1, 21, 3, 7        | 3
1, 7,  1, 7         | 7
1, 1, 1, 1          / 2² × 2² × 3 × 7 = 336 s

336 s ÷ 60 s =  5.6 min (5 min)
0.6 × 60 = 36 s

c) 5' 36''