The answer is in the sentence
double every 6 months
in 6 months there would be 250*2 = 500 crickets
in 1 year there would be 500*2 = 1000 crickets
in 1.5 years there would be 1000 *2 = 2000 crickets
in 2 years there would be 2000 *2 = 4000 crickets
3a+b+c
The perimeter is two times one side (to account for the opposite) and two times the adjacent side. So if the sides would be x and y, the perimeter would be 2*x + 2*y.
So, knowing that the sum is 16a+8b-6c, if we subtract the given side 5a+3b-4c from this, what remains is two times the "other" side:
16a+8b-6c - 2*(5a+3b-4c) =
16a+8b-6c -10a-6b+8c =
6a+2b+2c
half of that is
(6a+2b+2c)/2 = 3a+b+c
No he walks 7/10 of a mile
you have to make 2/5 have a common denominator with 3/10
so 2×2=4 (numerator)
2×5=10 (denominator)
4/10+3/10= 7/10
since you only add the numerator because the denominator makes it a like term
