Adam's age is a multiple of 10 this year.
His age 4 years ago was a multiple of 9.
Adam's age is between 40 and 50.
- In how many years' time will Adam's age be a multiple of 7?
- How many years ago was Adam's age a multiple of 9?
(a)
Multiple of 10: 10, 20, 30, 40
Multiple of 10 (-4): 6, 16, 26, 36
Multiples of 9: 9, 18, 27, 36
Adam's age this year = 40
Multiples of 7: 7, 14, 21, 28, 35, 42
Number of years' time when Adam will be a multiple of 7
= 42 - 40
= 2
(b)
Multiples of 9: 9, 18, 27, 36
Least number of years ago when Adam's age was a multiple of 9
= 40 - 36
= 4
Answer(s): (a) 2; (b) 4