Question

bob is 15 and susan is 21, find the ratio of his age to hers____________

Answer 1

so ratio of bob to susan=bob:susan
bob=15
susan=21
bob:susan=15:21
these are like fractions or equal signs so
15:21=5:7

ratio is 5:7

Answer 2

Ratios can be expressed with a colon, fraction bar, or the word 'to' inbetween.

Bob's age:Susan's age
Bob's age/Susan's age
Bob's age to Susan's age

Of course we can substitute their ages here to get our ratio.

15:21, 15/21, or 15 to 21.

Just like a fraction, it can be simplified.
If you multiply/divide the top and bottom by the same number the ratio stays the same, just like how 1/2 = 2/4 = 3/6.

15 and 21 are both divisible by 3, so our ratio 15:21 can simplify to 5:7.