Technique © :
Step 1. Realise the fact that if the plant is growing at 1/6th every 31 days, on 1st August its height is 1/7th (increase the denominator by one) the height than 31 days back on 1st July.
Step 2. Therefore 1/7th of 21 inches is 3 inches.
Step 3. Now subtract the answer in step 2 from 21 inches
21 – 3 =18 inches
Answer: The height of the plant on 1st July was 18 inches.
Note: If you want to mentally double check your answer is right, you can now work forward, starting at the height of 18 inches on 1st July and calculate 1/6th to arrive at the height of 21 inches on 1st August 18 x 1/6 = 3 inches. Therefore the height on 1st August is 18 + 3 = 21 inches
Time allowed: 30 seconds Time taken using the technique: 3 seconds
Time saved = 27 seconds [9/10th(90%) of time allowed by examiner]
Now that you have mastered how to answer the above question in only three seconds (90% of the time allowed), go ahead and try a similar question below:
WORK SHEET – Practice question
A tree by 1/5th of its previous height every fortnight (two weeks) and its height today is 30 cm. Find the height of the tree a fortnight ago from today.
STEP 1
STEP 2
STEP3