A mango juice is made by mixing water and mango concentrate in the ratio 9 : 7. If x litres of water and 3x litres of mango concentrate is mixed in 160 litres of mango juice, then the new ratio becomes 13 : 14. What is the quantity of the new mango juice (in litres)?
- (a)206
- (b)216
- (c)197
- (d)212
Answer
Why
Correct — B. Turn the ratio into litres before touching x.
160 litres split 9 : 7 is 16 parts, so one part is 10 litres:
water = 90 L, concentrate = 70 L
Add x litres of water and 3x of concentrate, and impose the new ratio:
(90 + x) ⁄ (70 + 3x) = 13 ⁄ 14
14(90 + x) = 13(70 + 3x)
1260 + 14x = 910 + 39x
350 = 25x → x = 14
New volume = 160 + x + 3x = 160 + 56 = 216 litres → option (b)
Why the others are wrong
- (a)206 — 206 − 160 = 46, but the liquid poured in is x + 3x = 4x litres, so the new total must exceed 160 by a multiple of 4. It cannot land on 206.
- (c)197 — 197 is odd, while 160 + 4x is even for every whole x. 197 − 160 = 37 is not a multiple of 4, so no amount of pouring reaches this total.
- (d)212 — 212 needs x = 13. Put x = 13 back and the mix is 103 : 109, not 13 : 14. Only x = 14 gives 104 : 112, which reduces to 13 : 14.
Concept
A ratio is not a quantity. Convert first: 9 : 7 over 160 litres means 16 equal parts of 10 litres, so 90 litres of water and 70 of concentrate.
Only then does the addition make sense. Water becomes 90 + x, concentrate 70 + 3x, and the stated new ratio 13 : 14 gives you one linear equation in one unknown.
The question then asks for the volume, not for x, so the last step is 160 + 4x — the commonest place to lose the mark after doing the algebra correctly.
The new ratio keeps water first, matching the original 9 : 7 order. With x = 14 the mixture is 104 litres of water to 112 of concentrate, which is 13 : 14.
Key facts
- In 160 litres split 9 : 7, one part is 10 litres, giving 90 litres of water and 70 of concentrate.
- Adding x and 3x litres raises the total by 4x, so the new volume is 160 + 4x.
- x = 14 makes the mixture 104 : 112, which reduces to 13 : 14.
- The answer, 216 litres, is 160 + 4(14).
Study next
Common traps
- Writing the new total as 160 + x instead of 160 + 4x.
- Flipping the new ratio and giving water 14 parts instead of 13.
- Answering with x = 14 rather than the quantity of juice the question asks for.
SSC states the starting mixture as a ratio and then disturbs it.
23 Sep 2024, 09:00, Quant Q.20 does it with 32 litres of milk and water at 5 : 3 and asks how much water reaches 50%. 10 Sep 2024, 16:00, Quant Q.11 compares two men's mixtures after each adds water.
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