Need help solving a question that includes ratios

Question

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?

Answer 1

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 $\;5x = \;?$.

Answer 2

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!).