Explain please:
the ratio of Mark's allowance to Jim's allowance is 3:7
The ratio of Mark's allowance to Wanda's allowance is 2:5. What is the ratio of Jim's allowance to Wanda's allowance?

Question

Explain please:
the ratio of Mark's allowance to Jim's allowance is 3:7
The ratio of Mark's allowance to Wanda's allowance is 2:5. What is the ratio of Jim's allowance to Wanda's allowance?

phi · Answer

you know M/J   (it is 3/7)
you know M/W  (2/5)
what is J/W ?
one way to do this is "solve" for J  and solve for W, then take the ratio

phi · Answer

if M/J= 3/7 then (flip both)  J/M= 7/3
multiply both sides by M to get J= 7M/3
can you solve for W in
M/W = 2/5 
?

anonymous · Answer

Yes, w = 2m/5

phi · Answer

it looks upside down to me

anonymous · Answer

Right, sorry.
w = 5m/2

phi · Answer

now we do J/W
$$ \frac{\frac{7m}{3}}{\frac{5m}{2}} $$

anonymous · Answer

so 7m/3:5m/2
7/3:5/2
7/3*2/5
14/15?

phi · Answer

instead of dividing by 5m/2, multiply by 2/5m

phi · Answer

yes, that looks good

anonymous · Answer

Okay thank you.