H.C.F and L.C.M
Q41. The H.C.F and L.C.M of two numbers a and b are respectively 3 and 105. If a - b = 30, then (1/a) - (1/b) = ?
(a) -2/21
(b) -3/17
(c) -2/13
(d) -3/23
Answer: (a) -2/21
We have a X b = 3 X 105
⇒ ab = 315
| Now | a - b | = | 30 |
| ab | 315 |
| ⇒ | a | - | b | = | 2 |
| ab | ab | 21 |
| ⇒ | 1 | - | 1 | = | 2 |
| b | a | 21 |
| ⇒ | 1 | - | 1 | = | -2 |
| a | b | 21 |
Practice Test Exam