## Plain Number Math Drills

This is a sample of a practice Plain Number Math Drills. You might want to go back to the Consulting Math overview article for more in-depth information on improving your quantitative capabilities for the McKinsey PST and Case Interviews!

There are 8 types of Plain Number Math Drills.

Type 1:
Percentages

In a consulting context, people like to look at values, not only in absolute , but also relative to each other. Percentages become a very useful tool for consultants. As a consultant, you will very often find yourself doing back-of-the-envelope percentage calculations either in problem-solving meetings, in client interviews, or in your own analyses.
Therefore, it’s not surprising that this type of calculation is very common in Case Interviews and entrance tests (McKinsey PST & BCG Potential Test).

Exercise:

35% of 40,000?
20% of 1,250?
33% of 2.5 billion?
7.5% of 85?
4% of 1,340?

14,000
250
825,000,000 / 825 million
6.375
53.6

Type 2:
Multiplications

Besides additions and subtractions, multiplications are another important building block of calculating fundamentals. Multiplications are not only common in real life, but also in every aspect of business and consulting.
Therefore, it’s not surprising that this type of calculation is very common in Case Interview and entrance tests (McKinsey PST & BCG Potential Test).

Exercise:

4 x 920?
2.5 x 3,400?
85 x 23,000?
2,350 x 8?
350 x 12?

3,680
8,500
1,955,000
18,800
4,200

Type 3:
Increase in Percentage

In a consulting context, people like to look at values not only in absolute terms but also relative to each other. Percentages become a very useful tool for consultants. As a consultant, you will very often find yourself doing back-of-the-envelope percentage calculations either in problem-solving meetings, in client interviews, or in your own analyses.
Therefore, it’s not surprising that this type of calculation is very common in Case Interviews and entrance tests (McKinsey PST & BCG Potential Test).

Exercise:

900 increased by 54% would be…?
85,200 increased by 6% would be…?
2,400,000 increased by 75 % would be…?
265 increased by 0.2 % would be…?
6,200 increased by 15% would be…?

1,386
90,312
4,200,000
265.5
7130

Type 4:
Decrease in Percentage

Exercise:

200 decreased by 45% would be…?
73,500 decreased by 8% would be…?
8,500,000 decreased by 35 % would be…?
575 decreased by 0.6 % would be…?
7,400 decreased by 22% would be…?

110
67,620
5,525,000
571.55
5,772

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Type 5:
Currency Conversion-From USD

The world is getting smaller and international business is increasingly common. Along with that comes the need to do cross-country currency conversions in real consulting work.
Therefore, it is not surprising that this type of calculation is relatively common in Case Interviews and entrance tests (McKinsey PST & BCG Potential Test).

Below are the acceptable approximate conversion rates between US Dollars and the 7 most popular currencies in the world as of 2014. These conversion rates fluctuate day to day; however, there are still generally-accepted rates in most cases. These estimates are acceptable in Case Interviews unless the interviewer specifically instructs you to use more accurate rates.

Exercise:

\$12,500 USD equals … JPY?
\$15,000 USD equals … GBP?
\$300 USD equals … EUR?
\$7,500 USD equals … AUD?
\$2 million USD equals … SGD?
\$650 USD equals … CNY?
\$25,200 USD equals … INR?

1,250,000 JPY
9,000 GBP
225 EUR
8,250 AUD
2.5 million SGD
3900 CNY
1,512,000

Type 6:
Currency Conversion-To USD

Exercise:

250 GBP equals to…USD?
500 EUR equal to…USD?
7,400 AUD equal to…USD?
7,020 CNY equal to…USD?
15,400 INR equal to…USD?
600,000 SGD equal to…USD?
1,250,000 JPY equal to…USD?

\$416.6 USD
\$666.6 USD
\$6,727 USD
\$1,170 USD
\$256.6 USD
\$480,000 USD
\$12,500 USD

Type 7: Time Conversion
Though not very popular in Case Interviews and entrance tests (McKinsey PST & BCG Potential Test), calculations involving time units can be very tricky and time-consuming. Most units of time are easy to imagine and sense but very hard to do calculations with; this is because of their odd nature. There are only 60, not 100, seconds in a minute, 60, not 100, minutes in an hour, 24, not 25, hours in a day, 30, not 50, days in a month, 52, not 50, weeks in a year, etc.

Being skilled in this type of calculations will add value to your interviewing and test taking skillset!

When doing these practice calculations, please note that there are two different ways to calculate hours per week:

• (24/7): There are 24 hours per day and 7 days per week
• (Standard work hour): There are 8 hours per working day, and 5 working days per week

Exercise:

Assuming that there are 30 days per month and 365 days per year.

120 items per day equal to…items per hour? (24/7)
75,000 items per year equal to…items per week? (Standard work hours)
1,800 USD per month equal to …USD per day? (Standard work hours)
15 items per hour equal to…items per month? (Standard work hours)
25 USD per day equal to…USD per year? (24/7)

5 items
1,442.3 items
\$90 USD
2,400 items
9,125 USD

Type 8: Big Number Comfort
When people think of Management Consulting, usually they think of big projects, big clients, and big numbers. Almost all numbers floating around each project are big: big revenue, big production volume, big number of FTE (Full-time Equivalent) employees, big investments, big assets, etc. It is essential for all consultants to be comfortable working with big numbers. They have to be able to sense how big “big numbers” really are and perform big calculations with them.
Therefore, it’s not surprising that this type of calculation is very common in Case Interviews and entrance tests (McKinsey PST & BCG Potential Test).

Exercise:

500 thousand equals to…million?
6400 billion equals to…trillion?
1.5 trillion equals to…thousand?
0.06 trillion equals to…million?
450,000 thousand equals to… million?