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# GMAT: Math 14

76-80, pg. 162. Created by Sal Khan.

## Want to join the conversation?

• on question 76, when you reach 3.2/2 if you change it to 32/20 and do you division you will end up with 8/5 which is A, just seems shorter this way, right?
• #78: I don't understand why this doesn't work: 45*.85. The answer is 38.25 which is incorrect, but can someone explain the logic behind why it doesn't work?
(1 vote)
• This might get lengthy.
When you are doing 45*85 --> you are calculating a 15% reduction on the 45.
Let me give you an example:
An item costs 100\$ --> It increases by 20% to become 120\$. --> After the increment there is a discount and the (increased) price (120) is reduced by 20%.
20% of 120 = 24. Therefore reduction of 20% = 120-24 =96.
Which is equal to 120*80% = 96.
But since the original increase of 20% was applied to base of 100\$ and the decrease of 20% is applied to 120\$ the values of the 20%s are not equal.
In the same way, if you reduce 15% on the (already increased) 45m, it will not be the same amount as the original 15% increment.
Hope this clears your doubt, let me know if there are any more questions.
• How will this help me if I am in the 1st grade
• for number 79. where does the 2 come from? that is not a square root of anything....shouldnt it be 1, 4, 9, etc....
(1 vote)
• Bigger math = calculus? Well I dont know if it doesnt make sense grammatically or perhaps I just cant decipher what your answer is, but could you rephrase your answer?
• #78 another way.. 1.15* 38= 43 no1.15* 39= 44.85 yes( the nearst one 45 m)
To be sure you can multiply another numbers by 1.15
• For #79, where was he getting those numbers (1, 2, 4, 9, 16, 25, 36, 49)?
• Im thinking he meant to use 3 and not 2. @ he references the number 3 in his assessment of the number 9. 2 is just a typo.
(1 vote)
• in the beginning of question 78 why did you put an x?(im 12 years old,im studying this)