# Need help solving a question that includes ratios

Three groups, Group A, Group B, Group C, of Sam's friends decided to buy a watch as a memorable gift for his birthday. They contributed 1200 AED in the ratio of 3:4:5. How much did each group contribute?

Group A : Group B: Group C $\iff \;\;3:4:5 \iff 3x: 4x: 5x$.

$$3x + 4x + 5x = 1200\;\text{AED}$$

Solve for $x$: $$12 x = 1200 \iff x = 100\;\text{AED}$$ This gives us that

• Group A contributed $\;3x = 3\cdot 100 = 300 \;\text{AED}$,

• Group B contributed $\;4x = \;?$,

• Group C contributed $\;5x = \;?$.

• @Majid Since this answer seemed to help you, please feel free to accept the answer. To accept an answer (you can accept one answer per question asked), simply click on the grey $\checkmark$ to the left of the answer. It turns green, and you get 2 reputation points. – Namaste Nov 10 '13 at 16:33

The total amount of 1200 AED was devided in 12 parts. 3 parts are paid by group $A$, 4 parts by group $B$ and 5 parts by group $C$ (because the ratio is 3:4:5). Each part is $$\frac{1200}{12} = 100 \text{ AED}.$$ (The 12 parts of 100 AED make 1200 AED together.)

So group $A$ paid 3 parts of 100 AED, that is $3 \times 100$ AED $= 300$ AED. You can calculate the amount paid by $B$ and $C$ the same way (try it!).