The sum of the age of andy and his parents is 72.In how many years time will the sum of their age be 90?
3 answers
(90-72)/2 = 9
a = Andy's present age
m = Mom's present age
d = Dad's present age
m + d + a = 72
After x years:
Mom will be m + x yrs old
Dad will be d + x yrs old
Andy will be a + x yrs old
m + x + d + x + a + x = 90
m + d + a + 3 x = 90
We know:
m + d + a = 72
So:
72 + 3 x = 90 Subtract 72 to both sides
72 + 3 x - 72 = 90 - 72
3 x = 18 Divide both sides by 3
x = 18 / 3 = 6
After 6 years the sum of their age be 90.
m = Mom's present age
d = Dad's present age
m + d + a = 72
After x years:
Mom will be m + x yrs old
Dad will be d + x yrs old
Andy will be a + x yrs old
m + x + d + x + a + x = 90
m + d + a + 3 x = 90
We know:
m + d + a = 72
So:
72 + 3 x = 90 Subtract 72 to both sides
72 + 3 x - 72 = 90 - 72
3 x = 18 Divide both sides by 3
x = 18 / 3 = 6
After 6 years the sum of their age be 90.
I neglected the fact that there were two parents...
Always read the problem carefully!
Always read the problem carefully!
1 answer