Ques 1.
Six bells commencing tolling together toll at intervals of 2, 3, 6, 8 , 10 and 12 seconds respectively.In 30 minutes how many times do they toll together?
Ans 1.
L.C.M of 2, 4, 6, 8, 10 and 12 is 120. so, the bells will toll together after 120 seconds i.e. 2 minutes . In 30 minutes the bells toll together 30/2 + 1 times i.e. times.
Ques 2.
The H.C.F of two numbers is 11 and their L.C.M is 7700. If one of these numbers is 275, then find the other number. Ans 2.
Product of two number s = product of their H.C.F. and L.C.M. required number = 11 X 7700/275 = 308
Ques 3.
A gardener had a number of shrubs to plant in rows . At first he tried to plant 8, then 12 and then 16 in a row but he always had 3 shrubs left with him . On trying 7 shrubs he was left with none.Find the total number of shrubs.
Ans 3.
L.C.M of 8,12,16 = 48 Now, 48 x 1 + 3 = 51 – not divisible by 7 48 x 2 + 3 = 99 – not divisible by 7 48 x 3 + 3 = 147 – not divisible by 7 Required number = 147
Ques 4.
Three measuring rods are 64 cm,80 cm and 96 cm in length . What is the least length of cloth that can can be measured exact number of times using any one of these rods? (a) 9.60 m (b) 8 m (c) 9.60 cm (d) 96 m Ans 4. 9.60 m
Ans 4.
9.60 m
Ques 5.
The sum of two numbers is 528 and their H.C.F is 33. What is the number of pairs of such numbers ? (a) 4 (b) 12 (c) 8 (d) 6
Ans 5.
4 Hint : Let the number be 33x and 33y where x and y are co-prime.
