Question

If p:q=10:21 and q:r=6:5 find p:r.

Answer 1

Answer: p:r=4:7.

Explanation:

`\displaystyle\\1)\ p:q=(p)/(q) \\\\10:21=(10)/(21) \\\\Hence\\\\(p)/(q)=(10)/(21) \\\\2) \ q:r=(q)/(r) \\\\6:5=(6)/(5)\\\\Hence\\\\(q)/(r)=(6)/(5) \\\\\3)\ (p)/(q)*(q)/(r) =(p)/(r) \\(10)/(21) *(6)/(5) =(4)/(7) \\\\Hence\\\\p:r=4:7.`

Answer 2

6 = 2 × 3, 21 = 3 × 7

LCM of 6 and 21 = 2 × 3 × 7 = 42

p:q = 10:21 = 20:42

q:r = 6:5 = 42:35

p:r = 20:35 = 4:7