G1.3 If there are $c$ multiples of 7 between 200 and 500, find the value of $c$.
$\frac{200}{7}=28.6$, the least multiple of 7 is $7 \times 29=203$
$\frac{500}{7}=71.4$, the greatest multiple of 7 is $7 \times 71=497$ $497=a+(c-1) d=203+(n-1) \cdot 7 ; c=43$